A mixture partial credit model for identifying latent classes responsible for differential item functioning

AIMS : Ideally, the item response probability to a quality of life (QoL) questionnaire should only depend on the respondents’ QoL level. If such a probability also depends on other characteristics such as ethnicity, gender or socioeconomic status, differential item functioning (DIF) may be present. Identifying DIF plays a key role in verifying measurement invariance when validating questionnaires. Moreover, being able to take into account DIF allows limiting measurement biases when analyzing patient-reported ouctomes (PRO) data. Several methodologies have been proposed for dealing with DIF, one of the most flexible and powerful being the IRT-based likelihood ratio test. With such a method, the covariate suspected to be responsible for DIF on a given item can be identified. For this purpose, nested models (with and without DIF) are compared: one constrained to be DIF-free for the suspected item, and one considering DIF by including interactions between the item parameter and the considered covariate. The best model is then chosen for analyzing data, allowing taking into account DIF if necessary. However, some problems can occur when covariates responsible for DIF are not well identified. Multiple covariates can be wrongly suspected, leading in multiple comparisons thus in type I error rate inflation. Moreover, the covariate truly responsible for DIF might not be identified because it is not a directly observed covariate but a latent variable. METHODS : We propose an adaptation of the IRT likelihood ratio test based on mixture partial credit models (PCM). With these models, items parameters are considered as fixed effects and both the latent trait to be analyzed (for example QoL) and the covariate responsible for DIF are considered as continuous and categorical latent variables, respectively. Latent classes can finally be constructed based on such categorical latent variables using individual posterior probabilities, and then described using observed data. RESULTS : We illustrate the properties of such likelihood ratio test based on mixture PCM using both simulated data and observed data from the Pays-de-la-Loire Workers Surveillance Program (France), and provide a MPlus based macro-program working under Stata for performing such a procedure. CONCLUSIONS : We believe that such program may facilitate the use of these methods by researchers.

The challenge of measuring quality of life in children with Hirschsprung's disease or anorectal malformation

PURPOSE: The aim of the present study was to assess, after adaptation to French, the only specific quality of life (QoL) instrument for children with Hirschsprung\u27s disease or anorectal malformation, the Hirschsprung\u27s disease/Anorectal Malformation Quality of Life questionnaire (HAQL), in order to get a standardized QoL evaluation instrument that could further be used to help health care improvement. METHODS: The study was conducted in three teaching hospitals, including the French reference center for anorectal and pelvic malformations. After adaptation to French, QoL questionnaires were sent to the children and proxies. The questionnaire was mailed to 280 families. Psychometrics properties of the questionnaires (validity and reliability) were analysed from 120 proxy and 96 child questionnaires. RESULTS: The HAQL with the original structure was not acceptable. Exploratory steps led to a clinically pertinent structure that had acceptable fit and good validity and reliability properties. The final structure pools physical symptoms (continence, discomfort) and psychosocial dimensions (general well-being, social and emotional functioning) of QoL. CONCLUSION: The final structure, despite the disadvantage of being a new structure, allows assessment of QoL in this population and has the advantage of being shorter and validated on the clinical postoperative questionnaire from the Krickenbeck international consensus

The impact of anorectal malformations on anorectal function and social integration in adulthood: report from a national database.

AIM: The impact of anorectal malformation (ARM) on bowel function and social, educational and occupational end-points was investigated in adult patients entered on a national database. METHOD: Data from a national database of adult patients operated on between 1962 and 1999 for ARM were analysed. The database Malformations Ano-rectales et Pelviennes rares (MAREP) was part of a common information system, CEMARA, on rare congenital disorders. A self-administered questionnaire regarding bowel function, academic qualifications, employment and family status was mailed to patients. The type of ARM, subsequent follow-up and management including surgical interventions were retrospectively retrieved from medical records. RESULTS: Of 210 adult patients on the registry since 2008, 68 were included in this study. Only three (8.5%) had had regular follow-up. All reported some disturbance in bowel function. The fertility rate of 1.5 children per woman did not differ from the general population. CONCLUSION: Anorectal malformation ARM often leads to suboptimal bowel function in adulthood. This has an impact on social integration

Biases and power for groups comparison on subjective health measurements

Subjective health measurements are increasingly used in clinical research, particularly for patient groups comparisons. Two main types of analytical strategies can be used for such data: so-called classical test theory (CTT), relying on observed scores and models coming from Item Response Theory (IRT) relying on a response model relating the items responses to a latent parameter, often called latent trait. Whether IRT or CTT would be the most appropriate method to compare two independent groups of patients on a patient reported outcomes measurement remains unknown and was investigated using simulations. For CTT-based analyses, groups comparison was performed using t-test on the scores. For IRT-based analyses, several methods were compared, according to whether the Rasch model was considered with random effects or with fixed effects, and the group effect was included as a covariate or not. Individual latent traits values were estimated using either a deterministic method or by stochastic approaches. Latent traits were then compared with a t-test. Finally, a two-steps method was performed to compare the latent trait distributions, and a Wald test was performed to test the group effect in the Rasch model including group covariates. The only unbiased IRT-based method was the group covariate Wald\u27s test, performed on the random effects Rasch model. This model displayed the highest observed power, which was similar to the power using the score t-test. These results need to be extended to the case frequently encountered in practice where data are missing and possibly informative

Cyprus as an ancient hub for house mice and humans

© 2018 The Authors. Journal of Biogeography Published by John Wiley & Sons Ltd Aim: The distribution of the western house mouse (Mus musculus domesticus) around the world has been strongly influenced by the movement of humans. The close association between the house mouse and human phylogeography has been primarily studied in the peripheral distribution of the species. Here, we inferred the complex colonization history of Cyprus, situated close to the centre of the house mouse distribution and one of the first European islands to be colonized by the species. We investigated the resulting complexity of house mouse population genetics as well as considering the value of the house mouse as a bioproxy for studying modern human movement. Location: The study was carried out on Cyprus. Methods: The analysis was performed using 221 new mitochondrial D-loop sequences and assessed the fine-scale population genetic structure using 18 autosomal microsatellite loci from 191 modern house mice specimens. Results: We found a high genetic variability in the island that is illustrated by the presence of individuals from 9 of the 11 previously identified house mouse haplogroups for the D-loop, reflecting the hub-like nature of the island to mice. Two main waves of mouse introductions were tentatively identified based on coalescent and mismatch analysis. The first is apparently related to the Bronze Age expansion and the second one to more recent human movements. Cyprus represents an island with high complexity due to different introductions related to human transport and activity. Main conclusions: The dispersal of mice along with humans has left a complex footprint on the island with two main waves of introductions suggested. The phylogeography of the house mouse on Cyprus is in concordance with the complex human colonization history of the island and validates the use of the house mouse as a proxy to study human migration

Surgery for 'asymptomatic' mild primary hyperparathyroidism improves some clinical symptoms postoperatively

OBJECTIVE AND BACKGROUND: Most primary hyperparathyroidism (pHPT) patients do not conform to the guidelines for parathyroidectomy established by an international panel of specialists and have a mild pHPT. This group is typically defined as \u27asymptomatic\u27. The primary aim of this study was to determine symptom improvement in this \u27asymptomatic\u27 group after parathyroidectomy. Secondly, we aimed to create a preoperative clinical score predicting postoperative symptom resolution. DESIGN: A prospective nonrandomized study included patients with mild pHPT. METHODS: A questionnaire (22 items) was given to \u27asymptomatic\u27 patients preoperatively and at 3, 6, and 12 postoperative months. A logistic regression was performed to create a preoperative clinical score. RESULTS: One hundred and sixteen patients were included. Postoperatively, HPT was resolved in 98% of patients. Twelve of 22 nonspecific symptoms were improved at 1 year. Subgroups analysis showed a greater improvement in patients <70 years and those with a serum calcium level ≥2.6 mmol/l preoperatively. A clinical score, based on age and five symptoms, was established to predict the clinical improvement after surgery in mild pHPT patients with a positive predictive value of 81%. CONCLUSION: Patients with asymptomatic pHPT have clinical improvement of their symptoms postoperatively even after 1 year. Younger patients and those with higher preoperative calcium levels show the best improvement

A class of multidimensional IRT models for testing unidimensionality and clustering items

2PL model, EM algorithm, latent class model, NAEP data, Rasch model,