Modèle de mélange de lois multinormales appliqué à l'analyse de comportements et d'habiletés cognitives d'enfants

Cette étude aborde le thème de l’utilisation des modèles de mélange de lois pour analyser des données de comportements et d’habiletés cognitives mesurées à plusieurs moments au cours du développement des enfants. L’estimation des mélanges de lois multinormales en utilisant l’algorithme EM est expliquée en détail. Cet algorithme simplifie beaucoup les calculs, car il permet d’estimer les paramètres de chaque groupe séparément, permettant ainsi de modéliser plus facilement la covariance des observations à travers le temps. Ce dernier point est souvent mis de côté dans les analyses de mélanges. Cette étude porte sur les conséquences d’une mauvaise spécification de la covariance sur l’estimation du nombre de groupes formant un mélange. La conséquence principale est la surestimation du nombre de groupes, c’est-à-dire qu’on estime des groupes qui n’existent pas. En particulier, l’hypothèse d’indépendance des observations à travers le temps lorsque ces dernières étaient corrélées résultait en l’estimation de plusieurs groupes qui n’existaient pas. Cette surestimation du nombre de groupes entraîne aussi une surparamétrisation, c’est-à-dire qu’on utilise plus de paramètres qu’il n’est nécessaire pour modéliser les données. Finalement, des modèles de mélanges ont été estimés sur des données de comportements et d’habiletés cognitives. Nous avons estimé les mélanges en supposant d’abord une structure de covariance puis l’indépendance. On se rend compte que dans la plupart des cas l’ajout d’une structure de covariance a pour conséquence d’estimer moins de groupes et les résultats sont plus simples et plus clairs à interpréter.This study is about the use of mixture to model behavioral and cognitive data measured repeatedly across development in children. Estimation of multinormal mixture models using the EM algorithm is explained in detail. This algorithm simplifies computation of mixture models because the parameters in each group are estimated separately, allowing to model covariance across time more easily. This last point is often disregarded when estimating mixture models. This study focused on the consequences of a misspecified covariance matrix when estimating the number of groups in a mixture. The main consequence is an overestimation of the number of groups, i.e. we estimate groups that do not exist. In particular, the independence assumption of the observations across time when they were in fact correlated resulted in estimating many non existing groups. This overestimation of the number of groups also resulted in an overfit of the model, i.e. we used more parameters than necessary. Finally mixture models were fitted to behavioral and cognitive data. We fitted the data first assuming a covariance structure, then assuming independence. In most cases, the analyses conducted assuming a covariance structure ended up having fewer groups and the results were simpler and clearer to interpret

Validation de la version française canadienne du Perception of Prevalence of Aggression Scale auprès d’un échantillon d’intervenants en protection de la jeunesse

Objectif. L’objectif de cette étude est d’évaluer la validité de construit de la version française de l’échelle Perception Of Prevalence of Aggression Scale (POPAS), un questionnaire auto-rapporté mesurant l’exposition à la violence au travail commise par la clientèle du milieu de la santé et des services sociaux. Méthode. Un échantillon de 310 intervenants en protection de la jeunesse est utilisé afin de confirmer la structure interne à quatre facteurs de l’instrument. À défaut de confirmer cette structure, un modèle d’équation structurelle exploratoire est utilisé. Les facteurs retenus sont soumis aux tests d’alpha de Cronbach qui permettent d’évaluer leur cohérence interne. Ils sont corrélés avec la version française du Posttraumatic Stress Disorder Checklist Scale (PCLS) et du nombre de jours d’absence du travail causé par la violence afin d’évaluer la validité convergente. Il sont également corrélées avec le Felt Accountability (FA) afin d’évaluer la validité divergente. Des analyses de comparaison en fonction du lieu de travail permettent d’explorer la validité de critère. Résultats. L’analyse factorielle confirmatoire ne confirme pas la structure à quatre facteurs du POPAS. L’équation structurelle exploratoire valide une structure à trois facteurs : « violence verbale », « violence physique » et « violence envers soi-même ». Les deux premiers possèdent une bonne cohérence interne. Les corrélations positives entre ces deux facteurs et le PCLS, ainsi qu’entre ces deux facteurs et le nombre de jours d’absence appuient la validité convergente du POPAS. Toutefois, l’absence de corrélation significative entre le dernier facteur et le PCLS, et entre ce facteur et le nombre de jour d’absence n’appuient pas cette convergence. L’absence de corrélation des facteurs avec le FA appuie la validité divergente du POPAS. Les différences observées selon les environnements de travail attestent aussi de la validité de critère. Discussion. La validité de construit de la version française canadienne du POPAS suggère que l’outil permet d’évaluer la fréquence subjective de différentes formes de violence au travail vécues par les intervenants en protection de la jeunesse. Il offre ainsi une alternative aux données officielles (c.-à-d. déclaration d’incidents à l’employeur) qui reflètent peu la réalité de ces travailleurs compte tenu de la sous-déclaration des incidents de violence dans ce milieuObjective. The objective of this study is to evaluate the construct validity of the French Canadian version of the Perception Of Prevalence of Aggression Scale (POPAS), a self-report questionnaire measuring exposure to workplace violence committed by clients in the health and social services sector. Method. A sample of 310 youth protection workers is utilized to confirm the four-factor internal structure of the instrument. If this structure is not confirmed, an exploratory structural equation model is used. The selected factors undergo Cronbach alpha tests that assess their internal consistency. They are correlated with the French version of the Posttraumatic Stress Disorder Checklist Scale (PCLS) and the number of absentee days caused by violence in order to measure convergent validity. There are also correlated with the Felt Accountability (FA) scale to assess divergent validity. Comparison analyses according to work environments assess criterion validity. Results. The confirmatory factor analysis does not corroborate the four-factor structure of the POPAS. The exploratory structural equation model validates a three-factor structure: ‘‘verbal violence’’, ‘‘physical violence’’ and ‘‘violence against oneself’’. The first two possess good internal consistency. The positive correlations between these two factors and the PCLS, as well as between these two factors and the number of absentee days, support the convergent validity of POPAS. However, the absence of a significant correlation between the last factor and the PCLS, as well as between this factor and the number of absentee days, does not support convergence. The lack of correlation between the factors and the FA supports the divergent validity of the POPAS. The differences observed as they relate to work environments also attest to criterion validity. Discussion. The construct validity of the French Canadian version of the POPAS suggests that this instrument allows for an evaluation of the subjective frequency of different forms of workplace violence experienced by youth protection workers. It therefore represents an alternative to the use of official data (i.e. incident reports made to the employer), which poorly reflect the reality of these workers given the underreporting of violent incidents in this secto

StepMix: A Python Package for Pseudo-Likelihood Estimation of Generalized Mixture Models with External Variables

StepMix is an open-source software package for the pseudo-likelihood estimation (one-, two- and three-step approaches) of generalized finite mixture models (latent profile and latent class analysis) with external variables (covariates and distal outcomes). In many applications in social sciences, the main objective is not only to cluster individuals into latent classes, but also to use these classes to develop more complex statistical models. These models generally divide into a measurement model that relates the latent classes to observed indicators, and a structural model that relates covariates and outcome variables to the latent classes. The measurement and structural models can be estimated jointly using the so-called one-step approach or sequentially using stepwise methods, which present significant advantages for practitioners regarding the interpretability of the estimated latent classes. In addition to the one-step approach, StepMix implements the most important stepwise estimation methods from the literature, including the bias-adjusted three-step methods with BCH and ML corrections and the more recent two-step approach. These pseudo-likelihood estimators are presented in this paper under a unified framework as specific expectation-maximization subroutines. To facilitate and promote their adoption among the data science community, StepMix follows the object-oriented design of the scikit-learn library and provides interfaces in both Python and R.Comment: Sacha Morin and Robin Legault contributed equall

Capabilities of GPT-4 in ophthalmology: an analysis of model entropy and progress towards human-level medical question answering

Background: Evidence on the performance of Generative Pre-trained Transformer 4 (GPT-4), a large language model (LLM), in the ophthalmology question-answering domain is needed. // Methods: We tested GPT-4 on two 260-question multiple choice question sets from the Basic and Clinical Science Course (BCSC) Self-Assessment Program and the OphthoQuestions question banks. We compared the accuracy of GPT-4 models with varying temperatures (creativity setting) and evaluated their responses in a subset of questions. We also compared the best-performing GPT-4 model to GPT-3.5 and to historical human performance. // Results: GPT-4–0.3 (GPT-4 with a temperature of 0.3) achieved the highest accuracy among GPT-4 models, with 75.8% on the BCSC set and 70.0% on the OphthoQuestions set. The combined accuracy was 72.9%, which represents an 18.3% raw improvement in accuracy compared with GPT-3.5 (p<0.001). Human graders preferred responses from models with a temperature higher than 0 (more creative). Exam section, question difficulty and cognitive level were all predictive of GPT-4-0.3 answer accuracy. GPT-4-0.3’s performance was numerically superior to human performance on the BCSC (75.8% vs 73.3%) and OphthoQuestions (70.0% vs 63.0%), but the difference was not statistically significant (p=0.55 and p=0.09). // Conclusion: GPT-4, an LLM trained on non-ophthalmology-specific data, performs significantly better than its predecessor on simulated ophthalmology board-style exams. Remarkably, its performance tended to be superior to historical human performance, but that difference was not statistically significant in our study

Insomnie et risque suicidaire dans les troubles de la personnalité du groupe B : une étude comparative transversale

Objectif Le taux de mortalité par suicide parmi les personnes souffrant d’un trouble de la personnalité du groupe B (TPB) se situe autour de 20 %. La haute prévalence de comorbidités anxiodépressives ainsi que l’abus de substances majorent ce risque. Selon des études récentes, l’insomnie persistante serait aussi un facteur de risque suicidaire dans ce groupe clinique. Les mécanismes expliquant cette association sont peu connus. Il a été proposé que des facteurs psychopathologiques comme la dysrégulation émotionnelle ou l’impulsivité pourraient agir comme médiateurs dans ce lien entre l’insomnie et le suicide. Afin de bien comprendre la relation insomnie-suicide dans le TPB, il est important d’identifier le rôle des comorbidités.L’étude comporte deux objectifs. Le premier vise à comparer la sévérité des symptômes d’insomnie et le niveau d’impulsivité d’un groupe avec TPB à ceux d’un groupe contrôle, le deuxième tente d’établir les relations entre l’insomnie, l’impulsivité, les comorbidités anxiodépressives, l’abus de substance et le risque suicidaire. Méthode Étude transversale portant sur 138 patients (âge moyen = 33,74 ; 58,7 % femmes) ayant un TPB. Les données de ce groupe, obtenues à partir d’une base de données d’un institut en santé mentale québécois (banque Signature : www.banquesignature.ca) ont été comparées à celles d’un groupe de 125 sujets sains appariés sur l’âge et le sexe et sans historique de trouble mental. C’est à l’admission aux urgences psychiatriques que le diagnostic de TPB a été déterminé à l’aide d’une entrevue diagnostique et que des questionnaires autorapportés mesurant l’anxiété, la dépression, l’impulsivité et l’abus de substances ont été remplis par les participants. Les participants du groupe contrôle se sont rendus au centre Signature afin de compléter ces mêmes questionnaires. Une matrice corrélationnelle et une régression linéaire multiple ont été utilisées pour explorer les relations entre les variables.Résultats Le groupe avec TPB présentait des symptômes d’insomnie plus élevés et des niveaux d’impulsivité supérieurs par rapport au groupe contrôle, à l’exception du temps total de sommeil. Dans le modèle de régression, la satisfaction envers le sommeil, le manque de préméditation, l’urgence positive, la dépression et l’utilisation de substances étaient significativement associés aux scores au Suicidal Behavior Questionnaire-Revised (SBQ-R). Ce modèle expliquait 46,7 % de la variance des scores au SBQ-R.Conclusion Les résultats ont permis de mettre en évidence, pour la première fois, les éléments d’insomnie et d’impulsivité qui distinguent un groupe avec TPB par rapport à un groupe contrôle sain. Cette étude indique que l’insomnie et l’impulsivité pourraient être des facteurs de risque suicidaire dans le TPB, indépendamment des comorbidités et de l’utilisation de substances. De futures études permettront de vérifier la pertinence clinique potentielle de ces éléments de risque pour cette patientèle.Objective The suicide mortality rate among people suffering from cluster B personality disorders is estimated at approximately 20%. High occurrence of comorbid depression and anxiety, as well as substance abuse, are known contributors to this risk. Not only have recent studies indicated that insomnia may be a suicide risk factor, but it is also thought to be highly prevalent in this clinical group. However, the mechanisms explaining this association are still unknown. It has been suggested that emotion dysregulation and impulsivity may mediate the link between insomnia and suicide. In order to better understand the association between insomnia and suicide in cluster B personality disorders, it is important to consider the influence of comorbidities.The aims of this study were first to compare the levels of insomnia symptoms and impulsivity between a group of patients with cluster B personality disorder and a healthy control group and second, to measure the relationships between insomnia, impulsivity, anxiety, depression, substance abuse and suicide risk within the cluster B personality disorder sample. Methods Cross-sectional study including 138 patients (mean age = 33.74; 58.7% women) with cluster B personality disorder. Data from this group were extracted from a Quebec-based mental health institution database (Signature bank: www.banquesignature.ca) and were compared to that of 125 healthy subjects matched for age and sex, with no history of personality disorder. Patient diagnosis was determined by diagnostic interview upon admission to a psychiatric emergency service. Anxiety, depression, impulsivity and substance abuse were also assessed at that time point via self-administered questionnaires. Participants from the control group visited the Signature center to complete the questionnaires. A correlation matrix and multiple linear regression models were used to explore relations between variables.Results In general, more severe insomnia symptoms and higher levels of impulsivity distinguished the group of patients with cluster B personality from the sample of healthy subjects, although groups did not differ on total sleep time. When all variables were included as predictors in a linear regression model to estimate suicide risk, subjective sleep quality, lack of premeditation, positive urgency, depression level and substance use were significantly associated with higher scores on the Suicidal Questionnaire-Revised (SBQ-R). The model explained 46.7% of the variance of scores at the SBQ-R.Conclusion This study yields preliminary evidence indicating the possible implication of insomnia and impulsivity in suicide risk for individuals with cluster B personality disorder. It is proposed that this association seems to be independent of comorbidity and substance use levels. Future studies may shed light on the possible clinical relevance of addressing insomnia and impulsivity in this clinical population

Datasheet1_Inter-subject variability of pleasant pain relief using a data-driven approach in healthy volunteers.docx

BackgroundThe offset of a painful and unpleasant sensation can elicit pleasure. This phenomenon, namely pleasant pain relief (PPR), is attracting growing interest in research. While the cold pressor test (CPT) has been frequently used to study the inhibition of pain by the administration of another painful stimulation (inhibitory conditioned pain modulation; ICPM), a preliminary study from our research team has shown that CPT can also elicit a robust and long-lasting PPR. However, its effects on pain relief and inhibition vary greatly between subjects. Although substantial research has been carried out on inter-individual variability in the case of ICPM, the same cannot be said of PPR. Therefore, the current study sought to identify clusters of healthy volunteers with similar dynamic pain responses during the CPT, using a data-driven approach, and to investigate the inter-subject variability for PPR and ICPM.MethodsOne hundred and twenty-two healthy volunteers were recruited. A sequential ICPM paradigm was carried out with CPT (water at 10°C) and a Peltier Thermode to evaluate pain intensity and unpleasantness. Moreover, PPR was measured for four minutes at CPT offset. Statistical analyses were performed using group-based trajectory modelling.ResultsFour trajectories (groups) were identified for CPT pain intensity and unpleasantness ratings with varying levels of tonic pain and pain sensitization (e.g., temporal summation). PPR scores were correlated with both pain ratings trajectories (p DiscussionThis study has provided a first step into the investigation of PPR and ICPM interindividual variability. Using a data-driven approach, it was shown that PPR at CPT offset differs between clusters of participants identified based on dynamic pain intensity and unpleasantness responses from CPT. Thus, it was brought to light that both the levels of tonic pain and pain sensitization underlie individual differences in PPR. The lack of correlation between CPT pain trajectories and ICPM efficacy may be explained by the hypotheses that eliciting ICPM requires only a certain threshold of stimulation which doesn’t need to be noxious. In the future, studies on the inter-subject variability of PPR in large samples of chronic pain patients are warranted.</p