Statistical modelling studies examining the dimensional structure of psychopathology experienced by adults with intellectual disabilities: Systematic review

Abstract

Diagnosing mental ill-health using categorical classification systems has limited validity for clinical practice and research. Dimensions of psychopathology have greater validity than categorical diagnoses but dimensional models have not had a significant impact on our understanding of mental ill-health experienced by adults with intellectual disabilities. This paper systematically reviews the methods and findings from intellectual disabilities studies that use statistical methods to identify dimensions of psychopathology from data collected using structured assessments of psychopathology. The PRISMA framework for systematic review was used to identify studies for inclusion. Study methods were compared to best-practice guidelines on the use of exploratory factor analysis. Data from the 20 studies included suggest that it is possible to use statistical methods to model dimensions of psychopathology experienced by adults with intellectual disabilities. However, none of the studies used methods recommended for the analysis of non-continuous psychopathology data and all 20 studies used statistical methods that produce unstable results that lack reliability. Statistical modelling is a promising methodology to improve our understanding of mental ill-health experienced by adults with intellectual disabilities but future studies should use robust statistical methods to build on the existing evidence base.3

Problem behaviours and symptom dimensions of psychiatric disorders in adults with intellectual disabilities: An exploratory and confirmatory factor analysis

“…We believe our study is the first to develop and validate a dimensional model of psychopathology experienced by adults with intellectual disabilities using robust statistical methods (Melville et al, 2016). This is also the first study to compare the predictive validity of dimensional and categorical models of psychopathology in this population.…”

“…The three statistical models included categorical diagnosis (statistical model 1); dimensional scores (statistical model 2); a full model categorical diagnosis and factor/dimensional scores (statistical model 3). All three models included socio-clinical variables found to be associated with severity and outcome in a feasibility study (age, gender, level of intellectual disabilities, living circumstances, visual impairment, hearing impairment and incontinence; Melville, 2010). Since statistical models 1 and 2 were nested within statistical model 3, they were compared to the full model using the -2 log likelihood score and likelihood ratio test.…”

Prevalence of Challenging Behaviour in Adults with Intellectual Disabilities, Correlates, and Association with Mental Health

“…Sturmey et al [41] additionally concluded that CBs could not be viewed as depressive equivalents in their similar correlational study as there were no particular CBs reliably associated with depression. Melville et al [42] surmised that CB was not indicative of depression because the measurement items related to depression and CB were located in different factors of an analysis of the Psychiatric Present State-Learning Disabilities Examination Scale. Other researchers also found that CB was not associated with MH problems [43,44].…”

“…Due to a range of limitations, none of the existing research studies allowing an examination of the association between CB and MH can be considered definitive. The main limitations include fundamental differences in diagnostic constructs in the field of ID [42,53], inconsistent definitions of CB (as mentioned earlier, and [54]). overlap between these two problems [55•], and the practical challenges of categorical diagnoses in both clinical and research settings [56].…”

“…overlap between these two problems [55•], and the practical challenges of categorical diagnoses in both clinical and research settings [56]. In addition to these conceptual challenges, much of the research has been adversely affected by methodological limitations including modest sample sizes [42], cross-sectional designs [57], and tautological issues such as studying people with ID already diagnosed with a psychiatric condition to elicit the presentation of MH problems in people with ID [5•]. Latterly, some of the statistical approaches employed have been questioned due to a failure to control for confounding variables, the use of techniques unsuited to categorical data, and a failure to validate (confirm) exploratory factor analyses [38,42].…”