Abstract
BackgroundPerformance 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.MethodsA 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.ResultsOf 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.ConclusionsFour 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.
Highlights
Performance on psychometric tests is key to diagnosis and monitoring treatment of dementia
Ashford et al [46] applied Item response theory (IRT) techniques to identify the degree of Alzheimer’s disease (AD) severity at which individual items of the Mini mental state examination (MMSE) are lost and the rate at which they are lost at that level of severity
Most difficult items were the three memory items and “Orientation to date”, and “Serial sevens”. These findings suggest that the mental functions assumed to underlie performance of these itemsmemory and attention and calculation- are lost earliest in the progression of AD
Summary
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 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. The total score is used to aid diagnosis and to assess and monitor disease severity. This method is quick and simple to apply and is based on the premise of all test items reflecting a common unobservable trait or the simple summation of raw scores overlooks any differences between the items and information the pattern of response can provide. It may lead to an inaccurate estimation of cognitive impairment [2]
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