Eur J Pediatr (2011) 170:65–73 Table 1 Descriptive statistics for the covariates in the IROS data set after the propensity score matching Age child Gender child Education proxy Marital status proxy Mean (SD) Male Higher education or university Primary or secondary school Married/living together Single, widow(er) Control 9.99 (5.12) 85 (63.9%) 51 (38.3%) 82 (61.7%) 116 (87.2%) 17 (12.8%) Trauma 9.32 (5.34) 85 (63.9%) 48 (36.1%) 85 (63.9%) 107 (80.5%) 26 (19.5%) 67 p value for difference 0.29 0.80 0.18 Age is given in years, for the other covariates we give absolute numbers (and percentage between brackets). We further give p values for the differences between the two matched groups. For gender, no p value is available (NA) because exactly the same number of males and females were included in the trauma and control group [7]. In 38.6% of the patients, a serious to critical brain injury was scored (Abbreviated Injury Scale 1990). On the other hand, 17.9% had solely a minor to moderate injury of the extremities or pelvis. The median length of stay in hospital was 6 days (range 2–124 days). Circumstances of trauma were among others traffic in 35.7%, fall in 19.3% and burn in 12.8%. Paediatric Overall Performance Cate- gory (POPC) upon discharge was normal in 59.3%, mild disability in 27.9%, moderate disability in 7.9% and severe disability in 3.6% [11]. Trauma cases did not differ significantly from non-responders or excluded cases for ISS, gender, age or main diagnosis (t test for ISS or age, Fisher’s exact for difference in proportions). ICF and the IROS instrument The ICF is a classification of health in its broadest sense. It is cross-cultural developed and truly generic. Recently, a version for children and youngsters became available (ICF- CY) [39]. The ICF-CY, as the ICF, is a taxonomy and consists of four separate constructs: bodily dysfunction (b), structural changes (s), daily activity/participation (d) and environmental influences (e). Codes are made up using an alphanumeric system starting with the letter of the construct; followed by a first digit for the particular chapter, then two for the second level description, and finally an optional third level single digit, e.g. d4 mobility, d450 walking, d4502 walking on different surfaces. The nature of somebody’s functioning and health can thus be described in more or less detail. Severity scaling, by adding a number after the decimal point (e.g. 450.2), is similar for all items and inherently asymmetrically constructed: 0 none (0–4%), 1 mild (5–24%), 2 moderate (25–49%), 3 severe (50–95%) and 4 total (96–100%). IROS includes 54 questions representing 99 ‘second- level’ ICF-CY codes (e.g. d760 problems with family relations), as well as questions on medical consumption, family impact and environmental influences (Electronic Supplementary Material: IROS.wmf). In addition, four ‘sum’ scores (physical, mental, social and total) measure the overall burden of health problems on an 11-point adjectival scale between 0 ‘no burden’ and 10 ‘maximum burden’. For reasons of feasibility, many problems are only scored under a more general code, ending with 8 or 9: ‘otherwise or not further specified’, e.g. b729 problems with functions of joint and bones, other specified and unspecified, which then also covers for instance b710 problems with the mobility of joints. The 99 ICF codes used thus capture the whole spectrum of the ICF (and therefore of ‘health’) [32, 37]. Since several questions correspond to more than one code, space for free text clarification is provided. To promote uniformity in scaling, we added a scoring description sheet. Data structure and statistical methodology Given the unlimited amount of possible health states, grouping of codes and severity levels is necessary for any evaluation beyond individual consulting and for further statistical analysis. We grouped codes according to their ‘first level’, in line with the ICF construct (e.g. item D1 ‘learning’ covering all codes starting with d1, e.g. d160 focussing attention; see also the item list in Table 2). However, b1 and b2 were split arbitrary into two items, so that respectively emotional (b1a: [b130, b134 and b152]) and other mental (b1b) codes, as well as pain (b2a: [b280]) and other sensation (b2b) could be appreciated separately. We also created an item summarising all ‘family burden’ codes (F). Further, severity levels were regrouped to a three-point scale (0 ‘normal to mild’, 1 ‘moderate’ and 2 ‘severe to very severe’). The eventual score in each item was defined as the highest level of severity in any of the ICF codes that corresponded to that item. For the ‘burden’ questions, scores were merged to four categories (0–1, 2–3, 4–5, 6–10). First, to test for significant differences between the trauma and the control group, we used the Generalized Estimating Equations approach for ordinal data [16]. Statistical inference was obtained using the Wald test.