Trochanteric fractures in the elderly : the influence of primary hip arthroplasty on 1-year mortality Introduction The aim of the study was to compare the mortality risk and complication rate after operative treatment of pertrochanteric fractures with primary arthroplasty , dynamic hip screw -LRB- DHS -RRB- or proximal femoral nail -LRB- PFN -RRB- . Introduction While relative consensus exists about the treatment of femoral neck fractures for elderly patients , the optimal treatment for per - and intertrochanteric fractures is still under debate -LSB- 1 , 7 -RSB- . In a previous study of 1,173 patients with proximal femoral fractures it appeared that trochanteric fractures are still a challenge , as 1-year mortality risk and complication rate were considerably higher compared with femoral neck fractures -LSB- 7 -RSB- . As restoration of the preoperative ambulatory level correlated with survival rate after 1 year -LSB- 7 -RSB- and elderly patients are often unable to cooperate with partial weight bearing , the primary stability of the device is crucial to allow early mobilization to prevent cardio-pulmonal complications and thrombosis . Excessive collapse of the fracture site and varus displacement is a common problem of sliding hip screws combined with plates or femoral nails especially in elderly women who often suffer from osteoporosis and poor bone quality -LSB- 16 -RSB- . Therefore , primary arthroplasty was proposed by some authors -LSB- 4 , 10 , 28 -RSB- but their patient collectives ranging from 37 to 54 were to small to allow general recommendations . Because we used hip arthroplasty even for trochanteric fractures for a long time as a standard procedure -LSB- 7 , 26 -RSB- , we are now able to report on our experiences in a large number of patients . This study compares the mortality risks and 1-year postoperative complications between arthroplasty and osteosynthetic fixation -LRB- DHS or PFN -RRB- for intertrochanteric fractures . A 1-year mortality was chosen as a main indicator as it depends on the surgical trauma as well as the rapid return to preinjury activity and further complications . A 1-year period was chosen as the mortality risk approaches that of an age-matched reference population after this interval -LSB- 32 , 35 -RSB- . Patients and methods A total of 308 patients who were treated for trochanteric femoral fractures between 1992 and 2005 with a minimum age of 60 years were enrolled in this study . Seventeen patients with pathologic fractures due to metastases were excluded . Information about survival after 1 year could be achieved from 283 of the 291 patients . Two hundred and seventeen patients -LRB- 76.7 % -RRB- were female . The mean age at the time of surgery was 80.5 -LRB- ± 9 -RRB- years ranging from 60 to 98 years . Women -LRB- 82 ± 8 years -RRB- of our cohort were significantly older than men -LRB- 75.5 ± 11 years ; P < 0.01 -RRB- . The fracture type was classified according to the System of the Orthopedic Trauma Association -LRB- AO/OTA -RRB- -LSB- 24 -RSB- . Pertrochanteric two part fractures are classified as A1-type , multi-part fractures as A2-type and reversed oblique intertrochanteric fractures as A3-type fractures . While all A1-type fractures are considered to be stable , most of the A2 and all A3 type fractures are unstable -LSB- 19 -RSB- . The distribution of the fracture types within the treatment groups is displayed in Fig. 1 . Fig. 1Distribution of the surgical treatment depending on the fracture type . The dynamic hip screw -LRB- DHS -RRB- was mostly used in more stable fractures , while the proximal femoral nail -LRB- PFN -RRB- was mainly used in A3-type fractures -LRB- X ² = 22.4 , P < 0.001 -RRB- A total of 109 patients -LRB- 38.5 % -RRB- were treated with a `` dynamic hip screw '' -LRB- DHS by Synthes ® -RRB- . Within this group there were mainly stable fractures type A1 -LRB- 52 % -RRB- or A2 -LRB- 44 % ; Table 1 -RRB- ; 132 patients -LRB- 46.6 % -RRB- were treated with primary arthroplasty , 117 with a total hip replacement -LRB- THR -RRB- and 15 with a bipolar hemiarthroplasty -LRB- HA -RRB- . Since 2000 PFN -LRB- Synthes ® -RRB- was used in 42 of the 100 cases , mainly for unstable fractures in patients without advanced osteoarthritis . As demonstrated in Table 1 , these patients were younger and more frequently male -LRB- P < 0.05 -RRB- . Table 1Description of the baseline variables within the treatment groupsArthroplastyDHSPFNAge -LRB- years -RRB- 83 ± 779 ± 975 ± 12Number of patients13210942Gender Female 115 -LRB- 87 % -RRB- 80 -LRB- 73 % -RRB- 26 -LRB- 62 % -RRB- Male17 -LRB- 13 % -RRB- 29 -LRB- 27 % -RRB- 16 -LRB- 38 % -RRB- ≥ 4 comorbidities63 -LRB- 48 % -RRB- 56 -LRB- 51 % -RRB- 17 -LRB- 41 % -RRB- Fracture type A137 -LRB- 28 % -RRB- 57 -LRB- 52 % -RRB- 7 -LRB- 17 % -RRB- A282 -LRB- 63 % -RRB- 48 -LRB- 44 % -RRB- 29 -LRB- 69 % -RRB- A312 -LRB- 9 % -RRB- 5 -LRB- 4 % -RRB- 6 -LRB- 14 % -RRB- Year of injury 1992 -- 1999111 -LRB- 84 % -RRB- 72 -LRB- 66 % -RRB- 0 -LRB- 0 % -RRB- 2000 -- 200521 -LRB- 16 % -RRB- 37 -LRB- 34 % -RRB- 42 -LRB- 100 % -RRB- Outcome variables Primary outcome variable was the 1-year mortality risk -LRB- Table 2 -RRB- . Furthermore , the occurrence of complications which led to further interventions was analyzed in multiple regression analysis . These were dislocation of the hip , non-union of the fracture , cutting out of the hip screw , infections , thrombosis and hematoma . The Merle d'Aubigne test -LRB- 0 to 18 points -RRB- was used to assess the patients -LSB- 10 -RSB- . We further questioned whether the patients returned to their preoperative status -LRB- e.g. living at home -RRB- . Table 2The distribution of fracture type and treatment and its specific mortality1992 -- 19992000 -- 20051992 -- 2005nDeathMortality -LRB- % -RRB- nDeathMortality -LRB- % -RRB- nDeathMortality -LRB- % -RRB- A1711926 .829413.81002323.0 THR34926 .50034926.5 HA003133 .33133.3 DHS371027 .019315.8561323.2 PFN000 .0700.0700.0 A2952829 .5661319.71614125.5 THR652436 .96233.3712636.6 HA001218 .31218.3 DHS30413 .318211.148612.5 PFN0030826 .730826.7 A317635 .35120.022731.8 THR12541 .60012541.6 HA000000 DHS5120 .0005120.0 PFN005120 .05120.0 All fractures1835329 .01001818.02837125.1 THR1113834 .26233.31174034.2 HA0015213 .315213.3 DHS721520 .837513.51092018.4 PFN0042921 .442921.4 THR total hip replacement , HA hemiarthroplasty , PFN proximal femoral nail , DHS dynamic hip screw Surgical technique The proximal femoral nail -LRB- PFN by Synthes ® - Switzerland -RRB- or the dynamic hip screw -LRB- DHS by Synthes ® - Switzerland -RRB- was used according to the manufacturer 's instructions . For closed reduction the patients were positioned supine on a fracture table . Only 135 ° four hole-DHS plates without additional trochanteric stabilizing plates or tension band wires were used in this series . For hemiarthroplasty a standard cemented stem -LRB- Weller , Aesculap , Germany -RRB- and a bipolar head -LRB- DePuy , Leeds , England -RRB- were used . All femoral stems were cemented using the modern 3D generation cementing technique -LSB- 2 -RSB- . In cases of total hip replacement , a polyethylene cup -LRB- Aesculap ® , Germany -RRB- was cemented in the same manner -LRB- Fig. 3 -RRB- . Statistics First we performed univariate analysis of independent variables -LRB- age , sex , treatment , preoperative risk factors , etc. -RRB- and mortality using Fischer 's exact test for qualitative variables and ANOVA for quantitative variables . The homogeneity of variance was checked by Levene test . All tests were two-sided and a P ≤ 0.05 was considered to be significant . The influence of treatment on mortality was checked by a multiple logistic regression model adjusted for the presence of preoperative comorbidities -LRB- four or more vs. up to three -RRB- , fracture classification , age , gender , complications requiring revision surgery and year of surgery . We used RR additional to OR because the more frequent the outcomes becomes , the more the odds ratio will overestimate the risk ratio when it is more than 1 or underestimate the risk ratio when it is less than 1 -LSB- 34 -RSB- . Odds ratios -LRB- OR -RRB- were transferred to relative risks -LRB- RR -RRB- according to the method of Zhang et al. -LSB- 34 -RSB- with the formula : RR = OR / -LSB- -LRB- 1 − P0 -RRB- + -LRB- P0 × OR -RRB- -RSB- , where P0 is the incidence of the outcome in the nonexposed group -LRB- reference category -RRB- , and OR the odds ratio given by the multiple analysis . A RR < 1 refers to a factor category that is mitigating -LRB- decreasing -RRB- the risk of the outcome -LRB- e.g. dying -RRB- when present , an RR > 1 refers to a factor category that is increasing that risk when present compared with the reference category . All analyses were conducted with the SPSS statistic software for Windows 12.0 -LRB- SPSS , Chicago , IL , USA -RRB- . Results Surgery Eighty-five percent of our patients were operated within 1 day after admission . In the other cases , operation was delayed to improve the preoperative condition of the patient , e.g. by transfusion or change of medication . This was independent of the treatment groups -LRB- P = 0.307 -RRB- . Mean blood loss and operating time differed significantly depending on the type of operation . The mean blood loss for arthroplasty -LRB- 1,050 ± 700 ml -RRB- was significantly higher than for fixation with a DHS -LRB- 409 ± 360 ml -RRB- or PFN -LRB- 332 ± 277 ml ; P < 0.001 -RRB- . Implantation of a hip replacement took a mean of 115 ± 36 min , that of a DHS 73 ± 38 min and of a PFN 84 ± 32 min -LRB- P < 0.001 -RRB- including time for closed reduction on the extension rag . Fracture classification significantly influenced operating time if an arthroplasty was performed . It was 100 ± 24 min for A. 1 , 121 ± 39 min for A. 2 and 127 ± 26 min for A.3-fractures -LRB- P = 0.012 -RRB- . The blood loss was similarly influenced -LRB- 800 ± 460 ml for A. 1 , 1,200 ± 800 ml for A. 2 , 900 ± 500 ml for A. 3 fractures ; P = 0.019 -RRB- Mortality Six patients -LRB- 2.1 % -RRB- died during hospitalization , 25 -LRB- 8.9 % -RRB- within 90 days . These were patients with considerable preoperative risk factors ; 71 patients -LRB- 25.2 % -RRB- died within 1 year -LRB- Table 2 -RRB- . Influence of gender and age As demonstrated in Fig. 2 , survival was correlated to age and gender ; 34.8 % of the male and 24.9 % of our female patients dies within the first year -LRB- relative risk 0.34 , P = 0.004 ; Table 4 -RRB- . Not considering the different treatment groups patients over the age of 80 years had an increased mortality risk -LRB- P = 0.004 -RRB- . Fig. 2Influence of age and gender . Independent of the treatment and fracture type the mortality risk was significantly influenced by age for both genders -LRB- P = 0.018 for men , P = 0.002 for women -RRB- . After multivariate analysis , the risk to die was significantly lower for woman -LRB- relative risk 0.34 , P = 0.004 -RRB- and higher for patients over the age of 90 years -LRB- relative risk 3.61 ; P = 0.009 -RRB- Influence of comorbidities The comorbidities and their prevalence are shown in Table 3 . Of the single comorbidities only cardiac arrhythmia and cerebral diseases -LRB- P = 0.04 -RRB- showed a significant influence on mortality . Logistic regression analysis demonstrated that four or more comorbidities increased the risk to die by 78 % -LRB- relative risk 1.78 , P = 0.009 ; Table 4 -RRB- . Forty-eight percent of our patients had four or more comorbidities and showed a mortality risk of 33.3 % compared with 17.4 % if they had less than four -LRB- P = 0.032 in χ2-test -RRB- . Table 3The prevalence and relative risks of the most common comorbiditiesComorbiditynPoP -LRB- Fisher 's exact -RRB- RRORCI 95 % P -LRB- log . reg . -RRB- Heart attack1240 .3400.431.121.190.56 -- 2.140.69 Cardiac arrhythmia470 .3540.01 ** 1.101.161.02 -- 2.430.04 * Cardiac insufficiency1110 .3040.821.441.790.67 -- 3.180.55 Hypertonus1540 .2681.000.980.970.55 -- 1.730.92 Pulmonary diseases660 .2880.731.071.10.57 -- 2.160.77 Anemia470 .3190.351.261.430.69 -- 2.960.33 Renal insufficiency470 .2611.000.850.810.38 -- 1.750.60 Cerebral diseases1270 .3360.301.421.811.02 -- 3.220.04 * Diabetes mellitus920 .3260.281.241.410.79 -- 2.520.25 Metabolic diseases300 .2330.820.750.70.27 -- 1.800.46 Alcohol/nicotine/other drugs290 .3210.351.511.980.79 -- 4.990.14 Gastrointestinal disease420 .2440.310.760.710.32 -- 1.640.43 Others570 .3040.851.011.010.51 -- 2.030.96 Relative risks -LRB- RR -RRB- are computed from odds ratios -LRB- OR -RRB- by the following formula : RR = OR / -LSB- -LRB- 1 -- P0 -RRB- + -LRB- P0 × OR -RRB- -RSB- P0 is the proportion of patients with the respective disease dying within 1-year after proximal femoral fractureRR < 1.0 represents a minor risk of mortality ; RR > 1.0 represents a major risk of mortality compared with patients without this criteria ; * P ≤ 0.05 ; ** P ≤ 0.01 Table 4Multiple logistic regressions analysis of a 1-year mortality after proximal femoral fractures of elderly patientsDescription of the analysisInfluence of interaction of kind of treatment and fracture classification after adjusting age , gender , comorbidities , revision surgery and date of surgery Odds ratio95 % CIPRelative riskInfluence : interaction of kind of treatment and fracture classificatione A1 * PFN0 .0000.0000.9990.00 A1 * DHS0 .6380.228 -- 1.7870.3920.71 A2 * TEP1 .3910.566 -- 3.4200.4721.25 A2 * PFN1 .1240.272 -- 4.6470.8721.08 A2 * DHS0 .3720.112 -- 1.2370.1070.46 A3 * TEP2 .1200.502 -- 8.9540.3071.59 A3 * PFN1 .0170.087 -- 11.8330.9891.01 A3 * DHS1 .0930.096 -- 12.3870.9431.06 Influence : age categoryc 70 -- 79 years1 .2310.334 -- 4.5320.7551.19 80 -- 89 years2 .7980.785 -- 9.9700.1122.23 > 90 years6 .3811.603 -- 25.4030.0093.61 Influence : genderd Female gender0 .3380.161 -- 0.7080.0040.44 Influence : comorbidities complications and year of surgery ≥ 4 comorbidities2 .2381.219 -- 4.1090.0091.78 Revision surgery1 .1950.448 -- 3.1840.7221.13 Surgery after 20000.7750.343 -- 1.7520.5410.83 Relative risks -LRB- RR -RRB- are computed from OR -LRB- odds ratio -RRB- by the following formula : RR = OR / -LSB- -LRB- 1 − P0 -RRB- + -LRB- P0 × OR -RRB- -RSB- P0 is the proportion of patients in the respective reference category dying within 1-year after proximal femoral fractureRR < 1.0 represents a minor risk of mortality ; RR > 1.0 represents a major risk of mortality compared with patients without this criteriaNumber of cases in all models : 282aReference : TEPbReference : A1cReference : < 70 yearsdReference : male gendereReference : A1 * TEP Influence of fracture-classification and treatment Only pertrochanteric fractures were enrolled in this study and sorted according to the AO/OTA classification -LRB- Fig. 1 -RRB- . While the mortality did not differ between A1 - -LRB- 23.0 % -RRB- and A2-type fractures -LRB- 25.5 % -RRB- , it was higher in A3-type fractures -LRB- 31.8 % ; Table 2 -RRB- . As this fracture type affected only 7 % of our patients , it did not significantly influence the mortality risk -LRB- P = 0.42 -RRB- . About 18.4 % of the patients who received a dynamic hip screw , 21.4 % of those who received a proximal femoral nail and 33 % in the arthroplasty groups -LRB- THR and HA -RRB- died within 1 year -LRB- P = 0.011 -RRB- . As the indication for surgery was not randomized but decided on fracture classification and clinical status we attempted to reduce these influences in a multiple logistic regression analysis -LRB- Table 4 -RRB- . All potential influencing factors as gender , age , fracture type and amount of comorbidities were taken into account . If categorical variables were used to evaluate the interaction between fracture classification and treatment , we could not find a statistical influence of surgical treatment on mortality -LRB- Table 4 -RRB- . The relative risk to die was decreased for A. 1 - and A.2-type fractures , treated with a DHS , but this did not reach significance levels . As only seven patients with a A.1-type fracture were treated with a PFN -LRB- and all of them survived -RRB- , no sensible statistical analysis can be done for this category . As all devices showed good results for this kind of fracture , the decision should be based on other parameters for A.1-type fractures . Because our treatment regime was changed in the beginning of 2000 -LRB- introduction of the PFN , new bipolar hemiarthroplasty instead of total hip arthroplasty ; Table 2 -RRB- , we implicated the time of surgery in our analysis . Since then the 1-year mortality after arthroplasty decreased from 34.2 to 19 % -LRB- P = 0.26 , Fisher 's exact test -RRB- . Although over all mortality decreased from 29 to 18 % , no influence of time of surgery on the mortality risk could be found using multivariate regression analysis -LRB- P = 0.54 ; Table 4 -RRB- . Influence of complications The only postoperative complication which influenced the survival rate was postoperative pneumonia . It occurred in 13 cases independent of the treatment groups -LRB- P = 0.26 -RRB- . Six of the patients died within 1 year -LRB- P = 0.048 -RRB- . The DHS had a revision rate of 8.1 % , while the PFN needed reoperations in nine cases -LRB- 22.5 % -RRB- . The main reason was cutting out of the screw in the osteoporotic bone and postoperative hematoma . Due to cutting out and fixation failure secondary hip arthroplasty was performed after failed internal fixation ten times . It happened six times -LRB- 5.4 % -RRB- after a DHS and four times -LRB- 9.8 % -RRB- after a PFN . The main complication after arthroplasty was dislocation , which occurred in 16 patients -LRB- 12 % -RRB- . It did not occur with bipolar hemiarthroplasty . While dislocation was only a minor problem in A1-type fractures -LRB- 7 % -RRB- , it occurred in ten A2-type -LRB- 12 % -RRB- and two of the nine A3-type fractures -LRB- 22 % -RRB- . Patients were usually treated by closed reduction and physiotherapy and it did not influence mortality -LRB- P = 0.78 -RRB- . Rehabilitation The mean hospital stay was 18 days and did not differ significantly between the three treatment groups -LRB- P = 0.7 -RRB- . It prolonged to a mean of 30 days if a reoperation became necessary -LRB- P = 0.003 -RRB- . Patients who were ambulatory before the injury could walk with a walker or sticks at time of discharge ; 80 % of the surviving patients who were independent before the injury regained their preoperative status after 1 year . Since the year 2000 patients were encountered to a prospective registry . The mean Merle d'Aubigné score -LRB- 0 -- 18 points -RRB- for the surviving 78 patients was 13.8 ± 2.5 . No significant differences could be found between the three treatment groups -LRB- P = 0.122 -RRB- . Discussion While primary arthroplasty is a standard procedure for femoral neck fractures , little experience exists for trochanteric fractures -LSB- 4 , 5 , 9 , 28 -RSB- . They were primarily used as a salvage procedure after failed internal fixation -LSB- 12 , 15 , 21 , 23 , 31 -RSB- . Most authors implanted special calcar replacement devices , which are expensive and require the removal of large portions of the proximal femur -LSB- 3 , 8 , 13 , 28 -RSB- . We used a standard cemented stem and either a standard cemented cup or a bipolar head since the 1970s in our hospital . As it proved superior to former methods of internal fixation even for pertrochanteric fractures it was the treatment of choice since 1992 -LSB- 26 -RSB- . From the year 2000 on hemiarthroplasty was routinely used instead of total hip arthroplasty and the proximal femoral nail was introduced for patients without advanced osteoarthritis . The ideal treatment for intertrochanteric fractures is still under debate as none of the existing osteosynthetic devices could prove its superiority in former studies -LSB- 16 , 25 , 29 , 30 -RSB- . The most frequent problem in elderly patients who usually are not able to walk without weight bearing was a cutting out of the hip screw which occurred in 4 to 20 % of the reported cases -LSB- 4 , 6 -RSB- . In our series this complication was only seen in comminuted fractures -LRB- A2 and A3 type -RRB- . Thus , 10 times -LRB- 6.2 % of the internal fixation devices -RRB- a secondary hemiarthroplasty was performed . Immediate full weight bearing regardless of bone quality is an advantage of primary cemented arthroplasty . In our hospital , all patients are encouraged to stand up the day after surgery . Dislocation was the major complication in patients treated with a total hip replacement after comminuted pertrochanteric fractures . This high dislocation rate is rarely seen after primary hip arthroplasty but well known even for femoral neck fractures -LSB- 22 -RSB- or revision surgery -LSB- 33 -RSB- and can be attributed to insufficient muscular stability . Fractures of the greater or lesser trochanter might exaggerate this problem . The use of bipolar arthroplasty instead of total hip replacements can reduce this complication to an acceptable rate -LSB- 11 , 28 -RSB- . Since we use total hip arthroplasty only in patients of good physical shape with severe osteoarthritis we did not see any dislocations . Ambulatory levels and clinical scores are considerable affected by the preoperative status . Since clinical examination usually can not be obtained for all patients , reliable comparison is difficult . Some authors use telephone interviews -LSB- 4 -RSB- or report about less than 50 % of their patients for a 1-year follow-up -LSB- 10 -RSB- . In both cases it can be assumed that patients with bad functional results are not regularly included . We could also examine only 78 % of the last 100 patients clinically and therefore do not want to overemphasize these findings . Instead we chose the 1-year mortality risk as the primary outcome parameter as it could be obtained for all patients and is related to the postoperative ambulatory status as well as to the operative trauma -LSB- 14 -RSB- . In a previous study with more than 500 fractures , we could demonstrate that patients who regained their independency and were able to attend a rehabilitation institution had a significantly lower mortality risk -LSB- 7 -RSB- , which was further supported in this study . Mortality was significantly influenced by patient related factors such as gender , age and comorbidities but not by the fracture type . In accordance with our former studies and other authors -LSB- 7 , 17 , 20 , 26 -RSB- few single comorbidity influenced the mortality risk whereas the sum of four or more comorbidities increased the risk to die by approximately 78 % -LRB- Tables 3 and 4 -RRB- . Patients who received a PFN or DHS were significantly younger and healthier than those in the arthroplasty group . These influences were reduced by multivariate regression analysis -LRB- Table 4 -RRB- . Furthermore , the interaction of fracture type and treatment was taken into account . Considering these influences , no significant influence of one of the three treatment groups on the mortality risk could be found . In studies that only use internal fixation devices mortality risks comparable with our over all mortality were found -LSB- 27 -RSB- , thus -- in accordance with other authors -LSB- 3 , 13 -RSB- -- we think that cemented hemiarthroplasty is an alternative to internal fixation in elder patients especially as our revision rate was significantly lower for arthroplasty compared with internal fixation . Only Chan et al. -LSB- 4 -RSB- published a study about the use of a standard hemiarthoplasty for the treatment of displaced intertrochanteric fractures . In their small group of 54 patients they found a mortality rate of 31.5 % within 1 year which did not differ from comparable age-matched studies . The walking ability of their patients was favorable compared with other studies with internal fixation . We agree that immediate full weight bearing , which can be achieved after cemented arthroplasty , is crucial for these patients . Haentjens et al. compared 37 patients who received a calcar replacement device with 42 patients of a retrospective group , who were treated by internal fixation and found an advantage in functional outcome -LSB- 10 -RSB- . Although the mortality rate could not be decreased , early walking with full weight bearing reduced the incidence of pressure sores , pulmonary infection and atelectasis . Kim et al. -LSB- 18 -RSB- who compared a calcar replacement prosthesis with intramedullary fixation in a prospective study in two small groups of 29 patients could not find a significant difference concerning the functional outcomes , but the cut-out rate of the hip screw was 7 % in their patients . Up to now a clear indication of arthroplasty in the treatment of pertrochanteric fractures does not exist . Although operation time and blood loss are higher no significant difference concerning the mortality rate between primary arthroplasty and internal fixation could be found , but the revision rate in the arthroplasty group was significantly smaller especially since we use bipolar hemiarthroplasty instead of a total hip replacement . If the cemented arthroplasty has been performed accurately , there is very little concern about weight bearing . Furthermore , primary arthroplasty eliminates the possibility for malunion , cut-out of the hip screw and avascular necrosis of the femoral head . But primary arthroplasty is a technically challenging procedure . All lose fragments including the greater and the lesser trochanter have to be attached with cerclage wires before cementing the stem to prevent extrusion -LRB- Fig. 3 -RRB- and especially in utterly comminuted fractures orientation of the rotation and leg length can be demanding . Fig. 3Examples of treatment of A2-type fractures with a hemiendoprosthesis and tension band wires . Depending on the fracture type different ways of fixating the trochanteric region with wires were used . In the case of a calcar fragment reaching distal to the lesser trochanter a temporary reduction with a cerclage wire or reduction bone clamp was used before reaming . Final fixation of the greater trochanter was performed after reduction of the hip with cerclages or a tension band The DHS is not suitable for reverse oblique and comminuted fractures -LSB- 19 , 30 -RSB- but for stable fractures it seems to be advantageous to short femoral nails regarding reoperation rate and fracture fixation failure in the literature -LSB- 16 , 29 -RSB- . We further support the recommendation that the DHS should be used for stable A1 - and A2.1-type fractures while an intramedullary device is advantageous for unstable fractures . Primary cemented arthroplasty is a viable option for the treatment of trochanteric fractures in a selected group of previously independent mobile patients especially if osteoporosis would prevent full weight bearing or osteoarthritis would make further operations necessary . The routine use of total hip arthroplasty was abandoned in our hospital as the luxation rate was higher than after hemiarthroplasty . It is still used as salvage procedure after failed internal fixation in elder patients with bad bone quality .

O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O

mortality risk
trochanteric femoral fractures
total hip replacement


Assessment

and

Etiology

of

Attention

Deficit

Hyperactivity

Disorder

and

Oppositional

Defiant

Disorder

in

Boys

and

Girls

Attention

deficit

hyperactivity

disorder

-LRB-

ADHD

-RRB-

and

oppositional

defiant

disorder

-LRB-

ODD

-RRB-

are

more

common

in

boys

than

girls

In

this

paper

we

investigated

whether

the

prevalence

differences

are

attributable

to

measurement

bias

In

addition

we

examined

sex

differences

in

the

genetic

and

environmental

influences

on

variation

in

these

behaviors

Teachers

completed

the

Conners

Teacher

Rating

Scale-Revised

Short

version

-LRB-

CTRS-R

S

-RRB-

in

a

sample

of

male

and

female

Dutch

twins

No

sex

differences

in

the

factor

structure

of

the

CTRS-R

S

were

found

implying

the

absence

of

measurement

bias

The

heritabilities

for

both

ADHD

and

ODD

were

high

and

were

the

same

in

boys

and

girls

However

partly

different

genes

are

expressed

in

boys

and

girls

In

both

clinical

and

population

samples

children

diagnosed

with

attention

deficit

hyperactivity

disorder

-LRB-

ADHD

-RRB-

and

oppositional

defiant

disorder

-LRB-

ODD

-RRB-

are

predominantly

male

-LRB-

Gaub

and

Carlson

Biederman

et

al.

Loeber

et

al.

-RRB-

These

sex

differences

could

either

be

the

result

of

a

higher

liability

for

these

disorders

in

boys

than

girls

or

could

be

attributable

to

a

sex

effect

in

the

actual

measurement

of

the

phenotype

For

example

boys

and

girls

with

similar

levels

of

problem

behavior

may

receive

systematically

different

rating

scores

if

the

items

of

the

instrument

do

not

reflect

the

problem

behaviors

in

the

same

manner

in

boys

and

girls

This

may

conceptualized

as

bias

with

respect

to

sex

In

this

study

we

will

investigate

this

issue

in

the

measurement

of

ADHD

and

ODD

by

means

of

the

Conners

Teacher

Rating

Scale-Revised

Short

-LRB-

CTRS-R

S

-RRB-

version

The

presence

of

sex

differences

in

the

prevalence

of

ADHD

and

ODD

also

raises

the

question

whether

there

are

sex

differences

in

the

etiology

of

these

disorders

Sex

differences

in

etiology

can

only

be

interpreted

if

the

measurement

of

a

disorder

is

not

biased

with

respect

to

sex

Lubke

et

al.

-LRB-

-RRB-

discussed

in

detail

the

importance

of

establishing

unbiasedness

with

respect

to

sex

for

the

correct

interpretation

of

any

sex

differences

in

the

results

of

genetic

modeling

The

aim

of

this

paper

is

therefore

to

investigate

measurement

bias

in

teacher

ratings

of

ADHD

and

ODD

with

respect

to

sex

If

unbiasedness

can

be

shown

to

be

tenable

to

reasonable

approximation

we

shall

as

the

second

goal

of

this

paper

estimate

the

genetic

and

environmental

contributions

to

the

phenotypic

variance

in

ADHD

and

ODD

in

boys

and

girls

Mellenbergh

-LRB-

-RRB-

defined

unbiasedness

or

equivalently

measurement

invariance

-LRB-

MI

-RRB-

with

respect

to

group

to

mean

that

the

distribution

of

the

observed

test

score

conditional

on

the

latent

construct

that

the

test

measures

is

identical

over

groups

-LRB-

e.g.

boys

and

girls

-RRB-

In

more

simple

terms

this

means

that

the

instrument

is

measuring

the

same

construct

in

boys

and

girls

-LRB-

Mellenbergh

Meredith

-RRB-

If

this

is

the

case

we

expect

the

score

of

a

given

person

to

depend

on

that

person

's

score

on

the

latent

construct

but

not

on

that

person

's

sex

If

MI

does

not

hold

a

boy

and

a

girl

who

are

characterized

by

the

same

degree

of

problem

behavior

may

obtain

systematically

-LRB-

i.e.

regardless

of

measurement

error

-RRB-

different

scores

on

the

instrument

This

is

undesirable

because

we

wish

our

measurements

to

reflect

accurate

and

interpretable

differences

between

cases

in

different

groups

Analyses

aimed

explicitly

at

establishing

MI

with

respect

to

sex

according

to

the

approach

outlined

by

Meredith

-LRB-

-RRB-

have

yet

to

be

conducted

with

respect

to

ADHD

and

ODD

Although

MI

has

not

been

investigated

there

have

been

some

studies

which

addressed

sex

differences

in

the

factor

structure

in

teacher

ratings

of

ADHD

Fantuzzo

et

al.

-LRB-

-RRB-

examined

the

factor

structure

of

the

version

of

the

CTRS

with

exploratory

factor

analyses

They

reported

a

three-factor

solution

which

accounted

for

of

the

variance

The

factors

admitted

interpretations

in

terms

of

conduct

hyperactivity

and

passivity

The

invariance

of

the

factor

structure

was

established

by

comparing

results

from

random

subgroups

with

the

results

from

subgroups

based

on

sex

The

results

supported

the

similarity

of

the

factor

structure

across

sex

A

concern

in

this

study

is

that

the

subjects

in

this

study

were

children

from

classrooms

located

in

low-income

neighborhoods

It

is

therefore

unclear

how

representative

the

sample

is

of

the

general

population

Furthermore

because

each

teacher

rated

more

than

one

child

and

children

were

clustered

into

classes

the

assumption

of

independent

observations

which

is

important

in

statistical

inference

might

not

hold

In

this

study

we

conducted

confirmatory

factor

analyses

-LRB-

CFA

-RRB-

of

data

from

a

large

general

population

sample

of

twins

rated

by

their

teachers

on

ADHD

and

ODD

Two

questions

are

addressed

First

is

the

measurement

model

that

relates

differences

in

the

latent

constructs

of

ADHD

and

ODD

to

the

observed

behavior

problem

scores

identical

in

boys

and

girls

i.e.

is

MI

tenable

Second

do

the

magnitudes

of

the

genetic

and

environmental

influences

differ

or

do

different

genes

play

a

role

in

boys

and

girls

Methods

Subjects

and

procedure

This

study

is

part

of

an

ongoing

twin

study

of

development

and

psychopathology

in

the

Netherlands

The

subjects

were

all

registered

at

the

Netherlands

Twin

Registry

-LRB-

NTR

Boomsma

et

al.

-RRB-

We

assessed

a

sample

of

Dutch

twins

from

the

birth

cohorts

These

twins

were

assessed

by

their

teachers

when

they

were

years

old

The

twins

at

age

are

representative

of

Dutch

children

with

respect

to

their

scores

on

measures

such

as

the

Child

Behavior

Checklist

-LRB-

CBCL

van

den

Oord

et

al.

-RRB-

The

socioeconomic

status

of

the

parents

of

the

twins

was

somewhat

higher

than

the

level

in

the

general

Dutch

population

-LRB-

Rietveld

et

al.

-RRB-

When

twins

reached

the

age

of

years

parents

were

asked

to

provide

informed

consent

to

approach

the

teacher

Consent

was

given

by

of

the

parents

Teachers

of

these

pairs

received

a

questionnaire

by

mail

and

were

asked

to

return

it

to

the

NTR

by

mail

The

response

rate

of

the

teachers

was

CTRS

data

were

available

for

at

least

one

twin

in

twin-pairs

-LRB-

complete

pairs

-RRB-

The

maternal

CBCL-AP

scores

at

age

years

were

not

significantly

different

between

families

in

which

parents

provided

permission

to

approach

the

teachers

-LRB-

mean

SD

-RRB-

and

families

in

which

parents

did

not

do

so

-LRB-

mean

SD

t

-LRB-

-RRB-

p

-RRB-

However

mean

maternal

AP

ratings

were

significantly

higher

in

twins

whose

teachers

did

not

return

the

questionnaire

-LRB-

mean

SD

-RRB-

than

in

twins

whose

teachers

did

return

the

questionnaire

-LRB-

mean

SD

F

-LRB-

-RRB-

p

-RRB-

To

avoid

biased

test

results

due

to

statistical

dependency

of

the

twin

data

we

randomly

included

the

score

from

only

one

of

the

members

of

a

twin-pair

in

the

CFA

The

resulting

sample

for

CFA

consists

of

individual

twins

-LRB-

boys

and

girls

-RRB-

In

the

genetic

analyses

we

included

all

complete

twin-pairs

Data

were

available

for

both

members

of

a

twin-pair

in

MZ

male

DZ

male

MZ

female

DZ

female

and

DZ

opposite

sex

pairs

Some

twins

were

rated

by

the

same

teacher

-LRB-

pairs

-RRB-

while

the

remaining

twins

were

rated

by

different

teachers

-LRB-

pairs

-RRB-

The

genetic

analyses

accounted

for

potential

differences

between

same

and

different

teacher

ratings

by

using

the

model

developed

by

Simonoff

et

al.

-LRB-

-RRB-

Incomplete

twin-pairs

were

excluded

from

the

genetic

analyses

Measure

The

CTRS-R

is

a

widely

used

instrument

to

assess

behavior

problems

-LRB-

Conners

Conners

et

al.

-RRB-

The

CTRS-R

was

developed

by

factor

analyzing

a

large

set

of

items

and

including

items

that

load

highly

on

interpretable

common

factors

In

addition

to

the

scales

that

were

derived

based

on

factor

analysis

an

ADHD

index

was

included

This

index

comprises

the

best

items

for

distinguishing

children

with

ADHD

from

children

without

ADHD

as

assessed

by

the

Diagnostic

and

Statistical

Manual

of

Mental

Disorders

-LRB-

DSM-IV

American

Psychiatric

Association

Conners

-RRB-

The

short

version

of

the

CTRS-R

which

was

used

in

this

study

contains

items

from

the

following

scales

oppositional

-LRB-

ODD

five

items

-RRB-

cognitive

problems-inattention

-LRB-

IN

five

items

-RRB-

hyperactivity

-LRB-

HI

seven

items

-RRB-

and

the

ADHD

index

-LRB-

ADHD-I

items

-RRB-

One

of

the

items

-LRB-

item

excitable

impulsive

-RRB-

is

included

in

both

the

hyperactivity

scale

and

the

ADHD

index

The

items

are

rated

on

a

Likert

scale

for

symptom

severity

-LRB-

i.e.

not

true

at

all

just

a

little

true

pretty

much

true

very

much

true

-RRB-

The

internal

consistency

and

stability

of

the

CTRS-R

S

version

are

good

as

the

Cronbach

's

alpha

coefficients

range

from

to

and

test

retest

correlations

range

from

to

-LRB-

Conners

-RRB-

Distribution

of

the

items

Because

of

the

categorical

nature

of

the

item

scores

Pearson

product

moment

correlations

underestimate

the

correlation

of

the

underlying

latent

trait

and

consequently

the

parameter

estimates

obtained

in

factor

analyses

or

principal

component

analyses

based

on

the

Pearson

correlation

matrices

are

biased

-LRB-

Dolan

-RRB-

We

therefore

adopted

an

approach

that

is

suitable

for

factor

analyzing

discrete

item

scores

Polychoric

correlations

between

items

were

obtained

based

on

the

liability

threshold

model

-LRB-

Lynch

and

Walsh

-RRB-

In

the

case

of

a

Likert

scale

three

thresholds

divide

the

latent

liability

distribution

into

four

categories

Criteria

of

MI

The

criteria

of

MI

are

empirically

testable

in

the

common

factor

model

-LRB-

Meredith

-RRB-

MI

criteria

are

-LRB-

-RRB-

equality

of

factor

loadings

over

groups

-LRB-

-RRB-

equality

of

item

intercepts

over

groups

-LRB-

i.e.

differences

in

item

means

are

the

result

of

differences

in

factor

means

-RRB-

and

-LRB-

-RRB-

equality

of

residual

variances

-LRB-

i.e.

variance

in

the

observed

variables

not

explained

by

the

common

factor

-RRB-

over

groups

When

satisfied

these

restrictions

ensure

that

any

differences

in

the

mean

and

variance

of

the

observed

variables

are

due

to

differences

in

the

mean

and

variance

of

the

common

factor

For

ordinal

data

MI

can

be

tested

by

constraining

the

thresholds

and

factor

loadings

and

residual

variances

to

be

equal

in

boys

and

girls

These

constraints

allow

estimation

of

group

differences

in

the

means

and

variances

of

the

common

factor

To

this

end

the

mean

and

variance

of

the

common

factor

are

fixed

at

and

respectively

in

an

arbitrary

reference

group

We

chose

to

estimate

the

mean

and

variance

in

girls

and

to

use

boys

as

the

reference

group

In

doing

so

we

are

modeling

the

observed

group

differences

as

a

function

of

the

differences

in

the

latent

liability

Statistical

analyses

The

polychoric

correlation

matrices

of

the

items

of

the

four

subscales

were

calculated

using

Prelis

-LRB-

Jöreskog

and

Sörbom

-RRB-

All

CFA

were

performed

on

raw

data

using

Mx

-LRB-

Neale

et

al.

-RRB-

In

principle

factor

analysis

of

p

ordinal

items

can

be

carried

out

using

full

information

maximum

likelihood

-LRB-

FIML

-RRB-

estimation

However

this

requires

repeated

integration

of

the

p-variate

normal

distribution

which

can

become

computationally

demanding

even

with

as

few

as

items

We

therefore

estimated

the

model

parameters

using

marginal

maximum

likelihood

estimation

-LRB-

MML

Bock

and

Aitkin

-RRB-

MML

maximizes

the

likelihood

of

the

data

conditional

on

the

latent

trait

in

contrast

to

FIML

which

maximizes

the

unconditional

likelihood

The

advantage

of

MML

compared

to

FIML

is

that

it

is

computationally

much

less

demanding

To

test

if

the

Conners

scales

are

MI

with

respect

to

sex

the

factor

structure

was

constrained

to

be

identical

in

boys

and

girls

The

ODD

IN

and

HI

scales

resulted

from

factor

analyses

and

a

single

factor

was

fit

to

these

scales

In

contrast

the

ADHD-I

contains

items

related

to

problems

with

inattention

and

hyperactivity

and

thus

a

two-factor

model

was

fitted

To

detect

prevalence

differences

in

ADHD

and

ODD

across

sex

the

means

and

variances

of

the

latent

factors

were

constrained

to

be

equal

in

boys

and

girls

The

fit

of

the

models

was

compared

by

χ

²

tests

with

a

type

I

error

probability

set

at

α

Browne

et

al.

-LRB-

-RRB-

noted

a

complication

of

the

χ

²

test

Specifically

they

showed

that

χ

²

is

influenced

by

the

unique

variances

of

the

items

If

a

trait

is

measured

reliably

the

inter-correlations

of

the

items

are

high

the

unique

variances

are

small

and

the

χ

²

test

may

suggest

a

poor

fit

even

when

the

differences

between

the

expected

and

observed

covariance

matrices

are

trivial

The

standardized

root

mean

square

residual

-LRB-

SRMR

Bentler

-RRB-

is

a

fit

index

that

is

not

sensitive

to

the

size

of

the

correlations

To

avoid

the

rejection

of

a

simpler

model

due

to

high

inter-item

correlations

we

only

reject

a

model

if

a

significant

χ

²

test

is

accompanied

by

large

residuals

-LRB-

SRMR

Hu

and

Bentler

-RRB-

After

investigating

MI

with

respect

to

sex

we

look

at

sex

differences

in

the

genetic

and

environmental

influences

on

the

individual

differences

in

the

sum

scores

of

the

scales

given

that

MI

is

tenable

-LRB-

Lubke

et

al.

-RRB-

The

polychoric

correlations

of

the

four

scales

were

calculated

by

sex

and

zygosity

in

PRELIS

-LRB-

Jöreskog

and

Sörbom

-RRB-

The

genetic

analyses

were

performed

on

the

raw

data

using

Mx

-LRB-

Neale

et

al.

-RRB-

With

data

from

MZ

and

DZ

twins

the

variance

in

behavior

can

be

attributed

to

genetic

and

environmental

factors

In

our

sample

of

the

twins

were

in

the

same

classroom

and

of

the

twins

were

in

different

classrooms

Correlations

between

twins

may

be

higher

when

children

are

rated

by

the

same

teacher

Therefore

a

correlated

error

model

developed

by

Simonoff

et

al.

-LRB-

-RRB-

was

used

to

analyze

the

data

In

this

model

individual

differences

in

behavior

are

explained

by

additive

genetic

factors

-LRB-

A

-RRB-

common

environmental

factors

that

are

shared

between

two

twins

of

a

pair

-LRB-

C

-RRB-

and

unique

environmental

factors

-LRB-

E

-RRB-

The

unique

environmental

factors

are

allowed

to

correlate

in

twins

who

are

placed

into

the

same

classroom

and

do

not

correlate

in

twins

who

are

placed

into

different

classrooms

For

the

genetic

analyses

the

items

of

each

subscale

were

summed

and

the

sum-score

was

recoded

so

that

three

thresholds

divide

the

latent

liability

distribution

into

four

categories

The

thresholds

were

chosen

in

such

a

way

that

the

categories

contain

more

or

less

equal

numbers

of

subjects

We

preferred

this

procedure

to

the

analysis

of

the

raw

sum

scores

because

these

are

skewed

and

therefore

can

not

be

analyzed

with

maximum

likelihood

approaches

based

on

the

assumption

of

normality

-LRB-

Derks

et

al.

-RRB-

Sex

differences

in

genetic

and

environmental

influences

were

examined

in

two

ways

First

we

investigated

if

the

estimates

of

the

genetic

and

environmental

variances

are

equal

in

boys

and

girls

Secondly

we

investigated

if

the

same

genes

influence

phenotypic

variation

in

boys

and

girls

These

qualitative

sex

differences

were

evaluated

by

constraining

the

genetic

correlation

in

opposite

sex

twins

at

-LRB-

similar

as

in

same-sex

DZ

twins

-RRB-

If

different

genes

play

a

role

in

boys

and

girls

the

genetic

correlation

is

expected

to

be

lower

than

in

opposite

sex

twins

Results

Measurement

invariance

We

tested

for

MI

by

constraining

the

factor

loadings

thresholds

and

residual

covariance

matrices

to

be

equal

for

boys

and

girls

while

allowing

the

factor

means

and

variances

to

be

different

The

factor

structure

of

ODD

was

MI

with

respect

to

sex

-LRB-

χ

²

-LRB-

-RRB-

p

SRMR

and

in

boys

and

girls

respectively

-RRB-

MI

was

also

tenable

for

the

ADHD-I

-LRB-

χ

²

-LRB-

-RRB-

p

SRMR

and

in

boys

and

girls

respectively

-RRB-

Both

IN

and

HI

showed

statistically

significant

different

factor

structures

in

boys

and

girls

-LRB-

χ

²

-LRB-

-RRB-

p

and

χ

²

-LRB-

-RRB-

p

respectively

-RRB-

However

the

residuals

between

expected

correlation

matrices

under

the

constrained

and

the

non-constrained

model

were

small

-LRB-

SRMR

in

girls

and

SRMR

in

boys

for

both

IN

and

HI

-RRB-

Apparently

the

lack

of

fit

was

the

result

of

the

high

inter-correlations

between

the

items

-LRB-

Browne

et

al.

-RRB-

and

not

of

large

residuals

between

the

expected

covariance

matrices

Therefore

we

tentatively

accept

MI

with

respect

to

sex

Table

provides

the

factor

loadings

and

thresholds

of

the

best-fitting

models

We

also

included

the

factor

loadings

as

reported

by

Conners

-LRB-

-RRB-

to

facilitate

the

comparison

of

our

sample

with

the

sample

that

was

used

to

create

the

scales

Note

that

the

factor

loadings

as

reported

by

Conners

-LRB-

-RRB-

are

generally

much

lower

as

these

estimates

are

based

on

the

assumption

of

a

continuous

normal

distribution

of

the

item

scores

an

assumption

that

is

obviously

violated

in

the

instance

of

a

four-category

Likert

scale

Table

rotated

factor

loadings

and

thresholds

-LRB-

T

-RRB-

of

the

best-fitting

factor

model

for

the

four

subscales

of

the

CTRS-R

SItemsLoadings

factor

factor

as

reported

by

Conners

-LRB-

-RRB-

-LRB-

N

-RRB-

Cognitive

Forgets

Poor

Poor

Lacks

Poor

Always

on

the

Leaves

Difficulty

Runs

Difficulty

ADHD

Attention

Only

pays

Fails

to

Not

follow

Remain

Interrupts

Excitable

Restless

AP

attention

problems

HI

hyperactivityThe

thresholds

are

constrained

to

be

equal

in

boys

and

girls

The

means

and

variances

of

the

latent

factors

in

boys

are

constrained

at

and

respectively

The

means

and

variances

of

the

latent

factors

are

freely

estimated

in

girls

The

variances

in

girls

were

not

significantly

different

from

The

means

of

the

latent

factors

are

estimated

at

-LRB-

oppositional

-RRB-

-LRB-

hyperactivity

-RRB-

-LRB-

ADHD-I

AP

-RRB-

and

-LRB-

ADHD-I-HI

-RRB-

The

mean

of

the

cognitive

problems-inattention

factor

is

not

significantly

different

between

boys

and

girls

Genetic

analyses

Having

established

MI

of

the

CTRS-R

S

scales

with

respect

to

sex

we

estimated

the

twin-correlations

and

carried

out

a

genetic

analysis

of

the

data

Twin

correlations

are

shown

in

Table

for

same

and

different

teachers

respectively

The

genetic

model

fitting

results

of

the

four

scales

are

reported

in

Table

All

correlations

are

higher

in

MZ

twins

than

in

DZ

twins

suggesting

the

presence

of

genetic

influences

on

individual

differences

The

correlations

are

higher

in

twin

pairs

rated

by

the

same

teacher

than

for

twin

pairs

rated

by

different

teachers

This

was

taken

into

account

by

using

a

correlated

error

model

-LRB-

Simonoff

et

al.

-RRB-

The

lower

correlations

in

opposite-sex

DZ

twins

than

in

same-sex

DZ

twins

suggest

that

different

genes

play

a

role

in

boys

and

girls

Table

twin-correlations

of

the

CTRS

rated

by

same

teachers

-LRB-

ST

-RRB-

versus

different

teachers

-LRB-

DT

-RRB-

OppositionalCognitive

problems-inattentionHyperactivityADHD

indexSTDTSTDTSTDTSTDTMonozygotic

Dizygotic

Monozygotic

Dizygotic

females0.660.100.600.420.340.250.450.24Opposite-sex

Table

model

fitting

results

on

CPRS-R

S

LLWith

modelΔdfΔχ

²

pOppositional

behavior

in

Fully

Equal

correlations

same

and

different

ACE

model

estimates

of

ACE

are

allowed

to

be

different

between

same

and

different

ACE

ACE

same

teacher

ACE

different

Correlated

errors

ACE

Correlated

errors

AE

Correlated

errors

AE

model

AE

boys

AE

Correlated

errors

AE

model

AE

boys

AE

girls

opposite-sex

genetic

Cognitive

problems-inattention

in

Fully

Equal

correlations

same

and

different

ACE

model

estimates

of

ACE

are

allowed

to

be

different

between

same

and

different

ACE

ACE

same

teacher

ACE

different

Correlated

errors

ACE

Correlated

errors

AE

Correlated

errors

AE

model

AE

boys

AE

Correlated

errors

AE

model

AE

boys

AE

girls

opposite-sex

genetic

Hyperactivity

in

Fully

Equal

correlations

same

and

different

ACE

model

estimates

of

ACE

are

allowed

to

be

different

between

same

and

different

ACE

ACE

same

teacher

ACE

different

Correlated

errors

ACE

Correlated

errors

AE

Correlated

errors

AE

model

AE

boys

AE

Correlated

errors

AE

model

AE

boys

AE

girls

opposite

sex

genetic

ADHD

in

Fully

Equal

correlations

same

and

different

ACE

model

estimates

of

ACE

are

allowed

to

be

different

between

same

and

different

ACE

ACE

same

teacher

ACE

different

Correlated

errors

ACE

Correlated

errors

AE

Correlated

errors

AE

model

AE

boys

AE

Correlated

errors

AE

model

AE

boys

AE

girls

opposite-sex

genetic

Model

fitting

analyses

showed

that

variation

in

all

four

scales

could

be

explained

by

additive

genetic

and

unique

environmental

effects

The

influences

of

the

shared

environment

were

not

statistically

significantly

The

magnitude

of

the

influences

of

genes

and

environment

did

not

differ

between

boys

and

girls

The

standardized

estimates

of

genetic

and

environmental

influences

are

shown

in

Table

Genetic

effects

explained

of

the

variation

in

the

CTRS

subscales

Unique

environmental

effects

explained

the

remaining

of

the

variation

For

all

four

scales

the

genetic

correlation

was

significantly

lower

than

in

opposite-sex

twins

This

implies

that

different

genes

are

expressed

in

males

and

females

The

genetic

correlation

in

opposite-sex

twins

was

for

oppositional

behavior

for

cognitive

problems-inattention

for

hyperactivity-impulsivity

and

for

the

ADHD

index

Table

estimates

of

the

genetic

and

environmental

effects

on

problem

behavior

Additive

genetic

effects

-LRB-

A

-RRB-

Non-shared

environmental

effects

-LRB-

E

-RRB-

Genetic

correlation

opposite-sex

Cognitive

ADHD

Discussion

The

purpose

of

this

study

was

twofold

First

we

investigated

if

teacher

ratings

on

ADHD

and

ODD

are

measurement

invariant

with

respect

to

sex

Secondly

genetic

and

environmental

influences

on

variation

in

ADHD

and

ODD

were

compared

between

boys

and

girls

Measurement

invariance

Teacher

ratings

on

ADHD

and

ODD

were

found

to

be

measurement

invariant

with

respect

to

sex

In

other

words

teacher

assessments

of

these

behavior

problems

relate

to

the

same

latent

variables

in

boys

and

girls

Sex

differences

in

observed

scores

on

ADHD

and

ODD

can

therefore

be

interpreted

as

differences

with

respect

to

the

latent

construct

This

supports

the

contention

that

the

reported

sex

differences

in

ADHD

and

ODD

-LRB-

Gaub

and

Carlson

Loeber

et

al.

Maughan

et

al.

-RRB-

are

due

to

a

higher

liability

for

the

disorder

in

boys

than

girls

and

not

to

measurement

bias

Quantitative

and

qualitative

differences

in

the

heritability

among

boys

and

girls

More

than

half

the

variance

in

ADHD

and

ODD

in

boys

and

girls

is

attributable

to

genetic

influences

The

remaining

variance

is

attributable

to

unique

environmental

influences

The

magnitude

of

the

influences

of

genes

and

environment

is

the

same

in

boys

and

girls

However

part

of

the

variance

in

ADHD

and

ODD

is

attributable

to

different

genes

in

boys

and

girls

We

base

this

on

the

fact

that

the

genetic

correlation

between

DZ

opposite-sex

twins

was

significantly

lower

than

which

is

the

theoretical

value

-LRB-

in

the

absence

of

assortative

mating

-RRB-

if

the

same

genes

influence

behavior

in

boys

and

girls

We

observed

a

genetic

correlation

lower

than

in

DZ

opposite-sex

twins

for

oppositional

behavior

cognitive

problems-inattention

hyperactivity

and

the

ADHD

index

Few

studies

have

addressed

quantitative

and

qualitative

sex

differences

in

heritability

estimates

from

teacher

ratings

Saudino

et

al.

-LRB-

-RRB-

reported

qualitative

sex

differences

in

heritability

of

teacher

ratings

of

hyperactive

behavior

in

twins

They

did

not

report

any

quantitative

sex

differences

which

is

in

agreement

with

the

current

findings

Vierikko

et

al.

-LRB-

-RRB-

report

lower

correlations

in

opposite-sex

twins

than

in

same-sex

DZ

twins

of

teacher

ratings

of

hyperactivity-impulsivity

in

twins

However

both

genetic

and

shared

environmental

effects

were

found

to

contribute

to

the

phenotypic

variance

in

these

data

It

was

not

possible

to

determine

if

the

lower

opposite-sex

correlations

were

the

result

of

sex-specific

genetic

influences

or

sex-specific

shared

environmental

influences

although

the

presence

of

the

latter

appeared

more

likely

These

findings

disagree

with

the

current

results

in

the

sense

that

we

did

not

find

any

evidence

for

shared

environmental

influences

However

both

studies

suggest

that

teacher

ratings

are

influenced

by

partly

different

etiological

factors

in

boys

and

girls

The

finding

of

different

genetic

influences

in

boys

and

girls

in

teacher

ratings

stands

in

contrast

with

results

based

on

parental

reports

In

parent

ratings

qualitative

sex

differences

are

not

found

for

attention

problems

-LRB-

Rietveld

et

al.

-RRB-

or

ODD

-LRB-

Hudziak

et

al.

-RRB-

The

different

findings

in

parent

and

teacher

ratings

may

be

explained

by

the

fact

that

the

behavior

of

children

depends

on

the

context

in

which

they

are

observed

Apparently

inattentive

hyperactive

and

oppositional

behavior

of

boys

and

girls

are

influenced

by

partly

non-overlapping

factors

at

school

while

this

is

not

true

for

these

behaviors

at

home

The

finding

of

sex-specific

genetic

variation

has

implications

for

gene-finding

studies

of

ADHD

and

ODD

The

fact

that

the

genes

which

influence

the

behavior

of

boys

and

girls

do

not

completely

overlap

indicates

that

some

quantitative

trait

loci

may

explain

variation

in

boys

but

not

in

girls

and

vice

versa

Therefore

the

data

from

boys

and

girls

can

not

be

collapsed

when

studying

genetic

effects

in

teacher

ratings

In

the

NTR

teacher

data

are

collected

at

the

ages

and

years

The

sample

sizes

at

the

ages

and

are

currently

relatively

small

In

the

future

we

plan

to

address

the

issue

of

qualitative

sex

differences

in

teacher

ratings

in

a

longitudinal

framework

The

results

of

such

a

study

will

reveal

if

the

finding

of

sex

differences

in

the

specific

genes

that

play

a

role

is

also

present

in

older

children

Another

important

issue

that

may

be

addressed

is

the

MI

of

ADHD

with

respect

to

age

The

results

of

this

study

should

be

interpreted

in

the

light

of

the

following

limitations

First

we

did

not

replicate

the

factor

structure

of

the

CTRS-R

S

by

means

of

exploratory

factor

analyses

of

the

items

To

take

the

ordinal

nature

of

the

data

into

account

we

used

the

liability

threshold

model

-LRB-

Lynch

and

Walsh

-RRB-

We

limited

the

number

of

common

factors

to

keep

the

computational

burden

manageable

Therefore

we

performed

CFA

in

which

we

assumed

that

the

items

are

correctly

assigned

to

the

four

scales

and

that

cross-loadings

are

absent

Second

teacher

ratings

were

shown

to

be

measurement

invariant

with

respect

to

sex

but

this

finding

may

not

generalize

to

parent

ratings

The

correlations

between

Conners

parent

and

teacher

ratings

are

small

to

moderate

with

a

range

-LRB-

Conners

-RRB-

It

has

been

shown

that

parents

and

teachers

rate

partly

different

aspects

of

the

child

's

behavior

-LRB-

Derks

et

al.

in

press

Martin

et

al.

-RRB-

Future

studies

will

reveal

if

MI

is

also

tenable

in

parent

ratings

Assessment

of

ADHD

and

ODD

symptoms

through

teacher

reports

on

the

CTRS-R

S

provides

a

solid

starting

point

for

measuring

sex

differences

in

mean

scores

or

in

heritabilities

Variation

in

teacher

ratings

of

children

's

problem

behavior

is

mainly

influenced

by

genetic

factors

The

size

of

the

genetic

influences

does

not

depend

on

the

child

's

sex

but

partly

different

genes

are

expressed

in

boys

and

girls

Future

studies

should

reveal

if

these

findings

generalize

to

children

from

different

age

groups

O O O O O O O O O O O O O O O O O O O O O B O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O B O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O B O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O B O O O O O O O O O O O O O O O O O O O O B I O O O O B O B O O O O O O O B I O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O B O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O B O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O B O O O O O O O O O O O O O O O O B I O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O B O O O O O O O O O O O O O O O O O O O B O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O B O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O B O B O O O O O O O O O O O O O O O O O B O B O O O O O O O B I O O O B O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O B O B O O O O O O O O O O O O O O O O O O O O O O B I O B O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O B I O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O B O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O

adhd
odd
sex differences
measurement invariance