Item response theory analysis of cognitive tests in people with dementia:a systematic review

BACKGROUND: Performance on psychometric tests is key to diagnosis and monitoring treatment of dementia. Results are often reported as a total score, but there is additional information in individual items of tests which vary in their difficulty and discriminatory value. Item difficulty refers to an ability level at which the probability of responding correctly is 50%. Discrimination is an index of how well an item can differentiate between patients of varying levels of severity. Item response theory (IRT) analysis can use this information to examine and refine measures of cognitive functioning. This systematic review aimed to identify all published literature which had applied IRT to instruments assessing global cognitive function in people with dementia. METHODS: A systematic review was carried out across Medline, Embase, PsychInfo and CINHAL articles. Search terms relating to IRT and dementia were combined to find all IRT analyses of global functioning scales of dementia. RESULTS: Of 384 articles identified four studies met inclusion criteria including a total of 2,920 people with dementia from six centers in two countries. These studies used three cognitive tests (MMSE, ADAS-Cog, BIMCT) and three IRT methods (Item Characteristic Curve analysis, Samejima’s graded response model, the 2-Parameter Model). Memory items were most difficult. Naming the date in the MMSE and memory items, specifically word recall, of the ADAS-cog were most discriminatory. CONCLUSIONS: Four published studies were identified which used IRT on global cognitive tests in people with dementia. This technique increased the interpretative power of the cognitive scales, and could be used to provide clinicians with key items from a larger test battery which would have high predictive value. There is need for further studies using IRT in a wider range of tests involving people with dementia of different etiology and severity

Mapping analyses to estimate health utilities based on responses to the OM8-30 otitis media questionnaire

Purpose To investigate the statistical relationship between the OM8-30 health-related quality of life measure for children with otitis media with effusion (OME) and measures of health utility (Health Utilities Index [HUI] Mark 3 and Mark 2) and to develop models to estimate HUI3 and HUI2 health utilities from OM8-30 scores. Methods A placebo-controlled, randomised trial (GNOME) evaluating intranasal mometasone in 217 children with OME provided concurrent responses to OM8-30 and HUI at three time points. Ordinary least squares (OLS), generalised linear models and two-step regression analyses were used to predict HUI3 and HUI2 utilities based on OM8-30 facet and domain scores. Results OLS models including all nine OM8-30 facets with or without predicted hearing level (HL) produced the best predictions of HUI3 utilities (mean absolute error: 0.134 with HL and 0.132 without; R 2: 0.63 with HL and 0.596 without). An OLS model predicting HUI3 utilities based on the two OM8-30 domain scores, reported hearing difficulties, predicted HL, age and sex also produced accurate predictions. Conclusion Regression equations predicting HUI3 and HUI2 utilities based on OM8-30 facet and domain scores have been developed. These provide an empirical basis for estimating quality-adjusted life years (QALYs) for interventions in children with OME