bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nonparametric Item Response Theory Using Stata
Authors: Hardouin Jean-Benoit , Bonnaud-Antignac Angélique , Sébille Véronique 
Published: November 2018

Item response theory is a set of models and methods allowing for the analysis of binary or ordinal variables (items) that are influenced by a latent variable or latent trait—that is, a variable that cannot be measured directly. The theory was originally developed in educational assessment but has many other applications in clinical research, ecology, psychiatry, and economics. The Mokken scales have been described by Mokken (1971, A Theory and Procedure of Scale Analysis [De Gruyter]). They are composed of items that satisfy the three fundamental assumptions of item response theory: unidimensionality, monotonicity, and local independence. They can be considered nonparametric models in item response theory. Traces of the items and Loevinger's H coefficients are particularly useful indexes for checking whether a set of items constitutes a Mokken scale. However, these indexes are not available in general statistical packages. We introduce Stata commands to compute them. We also describe the options available and provide examples of output.
A Closer Examination of Three Small-Sample Approximations to the Multiple-Imputation Degrees of Freedom
Authors: Wagstaff David A. , Harel Ofer 
Published: November 2018

Incomplete data is a common complication in applied research. In this study, we use simulation to compare two approaches to the multiple imputation of a continuous predictor: multiple imputation through chained equations and multivariate normal imputation. This study extends earlier work by being the first to 1) compare the small-sample approximations to the multiple-imputation degrees of freedom proposed by Barnard and Rubin (1999, Biometrika 86: 948– 955); Lipsitz, Parzen, and Zhao (2002, Journal of Statistical Computation and Simulation 72: 309–318); and Reiter (2007, Biometrika 94: 502–508) and 2) ask if the sampling distribution of the t statistics is in fact a Student's t distribution with the specified degrees of freedom. In addition to varying the imputation method, we varied the number of imputations ( m = 5,10, 20,100) that were averaged over 500,000 replications to obtain the combined estimates and standard errors for a linear model that regressed the log price of a home on its age (years) and size (square feet) in a sample of 25 observations. Six age values were randomly set equal to missing for each replication. As assessed by the absolute percentage and relative percentage bias, the two approaches performed similarly. The absolute bias of the regression coefficients for age and size was roughly −0.1% across the levels of m for both approaches; the absolute bias for the constant was 0.6% for the chained-equations approach and 1.0% for the multivariate normal model. The absolute biases of the standard errors for age, size, and the constant were 0.2%, 0.3%, and 1.2%, respectively. In general, the relative percentage bias was slightly smaller for the chained-equations approach. Graphical and numerical inspection of the empirical sampling distributions for the three t statistics suggested that the area from the shoulder to the tail was reasonably well approximated by a t distribution and that the small-sample approximations to the multiple-imputation degrees of freedom proposed by Barnard and Rubin and by Reiter performed satisfactorily.
Faster Estimation of a Discrete-Time Proportional Hazards Model with Gamma Frailty
Authors: Farnworth Michael G. 
Published: November 2018

Fitting a complementary log-log model that accounts for gamma-distributed unobserved heterogeneity often takes a significant amount of time. This is in part because numerical derivatives are used to approximate the gradient vector and Hessian matrix. The main contribution of this article is the use of Mata and a gf2 evaluator to express the gradient vector and Hessian matrix. Gradient vector expression allows one to use a few different options and postestimation commands. Furthermore, expression of the gradient vector and Hessian matrix increases the speed at which a likelihood function is maximized. In this article, I present a complementary log-log model, show how the gamma distribution has been incorporated, and point out why the gradient vector and Hessian matrix can be expressed. I then discuss the speed at which a maximum is achieved, and I apply sampling weights that require an expression of the gradient vector. I introduce a new command for fitting this model. To demonstrate how this model can be applied, I will examine information on when young males first try marijuana.
Using the Margins Command to Estimate and Interpret Adjusted Predictions and Marginal Effects
Authors: Williams Richard 
Published: November 2018

Many researchers and journals place a strong emphasis on the sign and statistical significance of effects—but often there is very little emphasis on the substantive and practical significance of the findings. As Long and Freese (2006, Regression Models for Categorical Dependent Variables Using Stata [Stata Press]) show, results can often be made more tangible by computing predicted or expected values for hypothetical or prototypical cases. Stata 11 introduced new tools for making such calculations—factor variables and the margins command. These can do most of the things that were previously done by Stata's own adjust and mfx commands, and much more. Unfortunately, the complexity of the margins syntax, the daunting 50-page reference manual entry that describes it, and a lack of understanding about what margins offers over older commands that have been widely used for years may have dissuaded some researchers from examining how the margins command could benefit them. In this article, therefore, I explain what adjusted predictions and marginal effects are, and how they can contribute to the interpretation of results. I further explain why older commands, like adjust and mfx, can often produce incorrect results, and how factor variables and the margins command can avoid these errors. The relative merits of different methods for setting representative values for variables in the model (marginal effects at the means, average marginal effects, and marginal effects at representative values) are considered. I shows how the marginsplot command (introduced in Stata 12) provides a graphical and often much easier means for presenting and understanding the results from margins, and explain why margins does not present marginal effects for interaction terms.
EORTC QLQ-C30 Descriptive Analysis with the qlqc30 Command
Authors: Bascoul-Mollevi Caroline , Castan Florence , Azria David , Gourgou-Bourgade Sophie 
Published: November 2018

Health-related quality of life is often an endpoint in oncology clinical trials. The European Organization for Research and Treatment of Cancer (EORTC) developed the cancer-specific quality of life questionnaire (QLQ-C30), which includes five functions, nine symptoms, and a global health status. These questionnaires are completed by the patients themselves throughout the process of care. The recommended approaches for processing EORTC QLQ-C30 data are usually descriptive and graphic. Our aim was to develop a user-written command that provided an automatic descriptive analysis of EORTC QLQ-C30 data, consisting of profile plots per visit and longitudinal plots per functional and symptom scale.
Speaking Stata: Letter Values as Selected Quantiles
Authors: Cox Nicholas J. 
Published: November 2018

Letter values were introduced and named by J. W. Tukey in the 1970s as selected quantiles. The idea is to choose a small set of quantiles to characterize an ordered sample of values, quantiles that are each defined as either individual order statistics or the mean of two such statistics. The procedure is to start with the median, to continue with quartiles, and then with first and last octiles, and so on. At each step, approximate medians are identified of successively smaller tail fractions until the extremes, the minimum and maximum, are reached. As a historical aside, the same idea can be identified in work by Francis Galton from 1880. Letter values are supported by Stata through the official command lv, but that command is geared to letter-value displays and (arbitrarily) will compute no more than 21 letter values. A new command, lvalues, is introduced that supports calculation of letter values without such limits and is designed to save results in new variables for as many variables and distinct groups as are specified. Results may then be easily listed and (especially) plotted in pursuit of identification and comparison of distribution level, spread, and shape. Examples are given with emphasis on quantile plots.
Effectiveness of healthcare educational and behavioral interventions to improve gout outcomes: a systematic review and meta-analysis
Authors: Ramsubeik Karishma , Ramrattan Laurie Ann , Kaeley Gurjit S. , Singh Jasvinder A. 
Published: November 2018

Background: We aimed to systematically review the effectiveness of healthcare behavioral and education interventions for gout patients on clinical outcomes. Methods: We searched multiple databases to identify trials or observational studies of educational or behavioral interventions in gout. Risk of bias was assessed with the Cochrane tool for randomized control trials (RCTs) and the Newcastle–Ottawa Scale for observational studies. We estimated odds ratios (ORs) for categorical and standardized mean difference (SMD) for continuous measures using a random-effects model. Results: Overall, eight (five RCTs and three observational) studies met the inclusion criteria and examined pharmacist-led interventions ( n = 3), nurse-led interventions ( n = 3) and primary care provider interventions ( n = 2). Compared with the control intervention (usual care in most cases), a higher proportion of those in the educational/behavioral intervention arm achieved serum urate (SU) levels <6 mg/dl, 47.2% versus 23.8%, the OR was 4.86 [95% confidence interval (CI), 1.48, 15.97; 4 RCTs] with moderate quality evidence. Compared with the control intervention, a higher proportion of those in the educational/behavioral intervention arm were adherent to allopurinol, achieved at least a 2 mg/dl decrease in SU, achieved an SU < 5 mg/dl, had a reduction in the presence of tophi at 2 years, had improved quality of life as assessed with SF-36 physical component scores, had a higher knowledge about gout and higher patient satisfaction (moderate-low quality evidence). Conclusion: Educational and behavioral interventions can improve gout outcomes in the short-intermediate term. Randomized trials are needed to assess its impact on long-term gout outcomes.
Musculoskeletal pain and symptoms in pregnancy: a descriptive study
Authors: Kesikburun Serdar , Güzelküçük Ümüt , Fidan Ulaş , Demir Yasin , Ergün Ali , Tan Arif Kenan 
Published: November 2018

Background: Pregnancy-induced hormonal and physiologic changes increase the risk of musculoskeletal problems in pregnancy. The purpose of this report is to provide a comprehensive look at the musculoskeletal pain and symptoms experienced during pregnancy. Methods: A total of 184 women (mean age 30.9 ± 5.0 years) who gave birth in the obstetrics clinic of a tertiary hospital were included in the study. The participants who had given birth at 37–42 weeks of pregnancy (term pregnancy) and aged over 18 years were selected for participation. Basic demographic and clinical characteristics of the participants including age, body mass index, weight gained during pregnancy, education level, occupation, parity, sex of baby, and exercise habits were collected from the medical chart and face-to-face interviews. Musculoskeletal pain sites were defined as hand–wrist, elbow, shoulder, neck, back, low back, hip, knee, and ankle–foot in a diagram of the human body. The interviews with participants were performed to assess their musculoskeletal pain separately at each trimester follow-up visit. Results: The most frequent musculoskeletal complaints during pregnancy were low back pain ( n = 130, 70.7%), back pain ( n = 80, 43.5%), hand–wrist ( n = 61, 33.2%) and hip pain ( n = 59, 32.1%). The participants experienced musculoskeletal pain most in the third trimester except for elbow, shoulder and neck pain compared with the first and second trimesters ( p < 0.05). Conclusions: The results of the study suggest that numerous musculoskeletal problems may complicate pregnancy especially in the third trimester.
Continuous Glucose Monitoring Integration in Clinical Practice: A Stepped Guide to Data Review and Interpretation
Authors: Aleppo Grazia , Webb Kimberly 
Published: November 2018

Background:The advent of continuous glucose monitoring (CGM) technology has transformed the approach to diabetes care. Multiple CGM systems are commercially available and increased accuracy has allowed development of hybrid and automated insulin delivery systems. Evidence of CGM clinical benefits has also increased exponentially in the last decade.Methods:Literature search, review of professional guidelines, and consensus statements were used to guide the preparation of this article. The clinical benefits of both professional and personal CGM in clinical practice as well as barriers to wider adotpion were explored. A stepped approach to review and interpretation of CGM data is suggested for use in the clinician’s office regardless of the software used.Results:Although increasing, the use of CGM in patients with diabetes is still not widespread; multiple barriers are still in place, despite the approval of CGM systems for patients above the age of 2 years old, the extension of coverage for Medicare beneficiaries and the integration of CGM with multiple insulin pump systems. Integration of CGM technology in clinical practice presents various challenges, from concerns relative to time constraints during office visits to lack of systematic approach to interpretation of the data.Conclusions:Understanding the usefulness of personal and professional CGM, appropriate patient selection as well as patient and provider training are crucial for the expansion of CGM therapy use in clinical practice. Utilizing the proposed stepped approach to CGM review and interpretation may allow wider adoption of CGM with more effective and efficient office visits.
Anterior Cruciate Ligament Reconstruction Using a Bone–Patellar Tendon–Bone Graft With and Without a Ligament Augmentation Device: A 25-Year Follow-up of a Prospective Randomized Controlled Trial
Authors: Elveos Marlene Mauseth , Drogset Jon Olav , Engebretsen Lars , Brønn Raymond , Lundemo Trond Olav , Gifstad Tone 
Published: November 2018

Background: Various grafts and ligament augmentation devices (LADs) have been used in the search for optimal reconstruction of the anterior cruciate ligament (ACL). Purpose: To compare 25-year follow-up results after ACL reconstruction using a bone–patellar tendon–bone (BPTB) graft with or without the Kennedy LAD. Study Design: Randomized controlled trial; Level of evidence, 1. Methods: One hundred patients undergoing ACL reconstruction between 1991 and 1993 were randomized into 2 groups: reconstruction using a BPTB graft alone (BPTB group, 51 patients) or a BPTB graft with the Kennedy LAD (LAD group, 49 patients). The 25-year follow-up evaluation included a clinical knee examination, patient-reported outcome measures, and an assessment of radiological osteoarthritis (OA) according to the Ahlbäck classification. Additional outcomes were reruptures and knee arthroplasty. Results: Ninety-three patients (93%) were available for the follow-up evaluation: 48 patients in the BPTB group and 45 in the LAD group. Through telephone calls, 26 patients were excluded from further investigation because of reruptures and arthroplasty in the knee of interest; 67 patients were further investigated. A total of 43 of 44 (98%) and 42 of 44 (95%) patients had negative or 1+ Lachman and pivot-shift test results, respectively. The mean Lysholm score was 85 for the BPTB group and 83 for the LAD group. All mean Knee injury and Osteoarthritis Outcome Score (KOOS) subscale values were ≥73. There were no statistically significant differences between groups in any of these outcomes or regarding the Tegner score, radiological classification of OA, or number of ACL reruptures. Signs of radiological OA were detected in all patients, and severe radiological OA (Ahlbäck grade III, IV, or V) was detected in 32% of patients in the BPTB group and 21% of patients in the LAD group ( P = .37). There were 12 patients in the BPTB group and 7 in the LAD group who had documented reruptures ( P = .40). One patient in the BPTB group and 6 in the LAD group underwent knee arthroplasty ( P = .054). Conclusion: In the present study, there were no statistically significant differences between groups in any of the outcomes. After 25 years, 19% of patients had reruptures, 27% had severe radiological OA, and 7% underwent knee arthroplasty.
Detection of Age-Related Macular Degeneration by Portable Optical Coherence Tomography Operated by Nonexpert Personnel: Potential Use for Screenings
Authors: Cho Chris , Liu Melissa M. , Channa Roomasa , Zhang Alice Y. , Quigley Harry A. , Jefferys Joan L. , Scott Adrienne W. 
Published: November 2018

Purpose: The purpose of this study is to determine the sensitivity and specificity of detecting age-related macular degeneration (AMD) using portable optical coherence tomography (OCT) operated by nonexpert photographers on undilated patients. Methods: In this case-control study, 92 individuals were recruited from the glaucoma and retina clinics at the Wilmer Eye Institute (Johns Hopkins University, Baltimore, MD). Using the portable iVue (Optovue, Inc, Fremont, CA) spectral-domain OCT (SD-OCT), 2 nonexpert photographers acquired retina map scans on undilated eyes of all participants. In total, 33 AMD eyes and 105 control eyes were evaluated and graded by ophthalmologists masked to the diagnoses. Results: Detection of AMD on the portable OCT by ophthalmologists exhibited sensitivities of 0.91 and 0.94 and specificities of 0.88 and 0.89, for graders 1 and 2, respectively. A strong intergrader agreement was observed (κ = 0.87). Conclusions: Nonexpert photographers can use a portable OCT on undilated eyes to acquire images for the detection of AMD. These findings present the potential utility of implementing a portable OCT in community screenings for earlier detection and treatment of disease.
Long term follow-up demonstrating stability and patient satisfaction of minimally invasive punch technique for percutaneous bone anchored hearing devices
Authors: Sardiwalla Yaeesh , Jufas Nicholas , Morris David P. 
Published: November 2018

Objective Minimally Invasive Ponto Surgery (MIPS) was recently described to facilitate the placement of percutaneous bone anchored hearing devices. As early adopters of this new procedure, we sought to perform a quality assurance project using our own small prospective cohort to justify this change in practice. We chose to examine device stability and to gauge our patients’ perspective of the surgery and their overall satisfaction with the process. Methods A total of 12 adult patients who underwent MIPS between 2016 and 2017 with a minimum post-operative follow-up of 12 months were included in this study. A prospective MIPS research clinic was used to follow patients, assess the implant site soft tissue status and gather qualitative information through patient interviews and surveys. Results The mean (SD) soft tissue status score averages using the IPS Scale were low for inflammation 0.1 (0.1), pain 0.1 (0.1), skin height 0.2 (0.1) and total IPS score 0.4 (0.3) indicating minimal soft tissue changes. Patient experiences with MIPS were overwhelmingly positive in reports through the MIPS modified SSQ-8. All patients reported speedy recoveries and no long-term complications. There were zero device losses. Conclusion The series presented in this paper represents the first MIPS cohort with long term follow-up to be published to date in North America. Our findings conclude both device stability and patient satisfaction with no loss of fixtures. Consequently, we have adopted MIPS as our procedure of choice for the placement of all percutaneous BAHDs.
Double Fogarty balloon catheter technique for difficult to retrieve esophageal foreign bodies
Authors: You Peng , Katsiris Sandra , Strychowsky Julie E. 
Published: November 2018

Background Foreign body ingestion is common, especially in the pediatric population. Plans for retrieval should be tailored to the specific esophageal foreign bodies. Case presentation We present a difficult to retrieve esophageal foreign body in a 3-year-old girl who ingested a 2 cm glass pebble. Intraoperatively, attempts using conventional optical forceps and retrieval baskets were unsuccessful due to the size and smooth texture of the object. A novel strategy using double Fogarty embolectomy balloon catheters for retrieval of blunt esophageal foreign bodies was devised and described. Conclusion The double fogarty retrieval technique described appeared to be safe and efficacious, allowing for extraction of large esophageal foreign bodies under direct visualization.
Effect of Pregabalin on Radiotherapy-Related Neuropathic Pain in Patients With Head and Neck Cancer: A Randomized Controlled Trial
Authors: Jiang Jingru , Li Yi , Shen Qingyu , Rong Xiaoming , Huang Xiaolong , Li Honghong , Zhou Lizhi , Mai Hai-Qiang , Zheng Dong , Chen Ming-Yuan , Xu Yongteng , Li Jibin , Hui Xuan , Simone Charles B. , Gaertner Jan , Argyriou Andreas A. , Chow Edward , Chen Pingyan , Tang Yamei 
Published: November 2018

Purpose Neuropathic pain is an unavoidable treatment-related adverse event among patients with head and neck cancer who are undergoing radiotherapy. We aimed to test the efficacy and safety of pregabalin versus placebo in the treatment of radiotherapy-related neuropathic pain. Patients and Methods This randomized, double-blind, placebo-controlled trial was conducted in four centers in China. Eligible patients with a mean pain intensity score of 4 or more on an 11-point numeric rating scale were randomly assigned to receive either active treatment with a flexible dose of pregabalin or placebo for 16 weeks. The primary efficacy outcome was pain reduction measured on the numeric rating scale. Result There were 128 patients who received treatment as randomly assigned. Pain intensity reduction was 2.44 in the pregabalin arm and 1.58 in the placebo arm at week 16, yielding an adjusted mean difference of 0.87 (95% CI, 0.30 to 1.44; P = .003). In the pregabalin arm, 38 patients (59.4%) achieved at least 30% pain relief versus 21 (32.8%) in the placebo arm ( P = .006). Nineteen patients (29.7%) in the pregabalin group and five (7.8%) in the placebo group achieved 50% or greater pain relief ( P = .003). Total scores on the Profile of Mood States-Short Form, pain severity and functional interference of Brief Pain Inventory-Short Form, as well as the physiology and psychology domain of the WHO Quality of Life-BREF all were reduced significantly at week 16 in patients who received pregabalin compared with those who received placebo. There was no significant difference ( P = .29) in the incidence of experiencing at least one adverse event in the pregabalin arm (n = 35; 54.7%) versus the placebo arm (n = 29; 45.3%). Conclusion Patients treated with pregabalin with radiotherapy-related neuropathic pain had greater pain alleviation, better mood states, and higher quality of life compared with patients in the placebo group, with a good tolerability.