Practice effect and test-retest reliability of the Wechsler Memory Scale-Fourth Edition in people with dementia

The Wechsler Memory Scale-Fourth Edition (WMS-IV) has been widely used to assess memory function in people with dementia. The older adult battery of the WMS-IV includes four indices and seven subtests. The aims of this study were to examine the practice effect and test-retest reliability and calculate the reliable change index modified for practice (RCIp) for the indices and subtests of the older adult battery of the WMS-IV for people with dementia.

Fifty-six participants completed the WMS-IV twice, two weeks apart. The practice effect was investigated using effect size (Cohen's d) and bootstrapping mixed design analysis of variance while considering the severity of dementia. The test-retest reliability was estimated using intraclass correlation coefficient (ICC).

The results showed non-significant practice effects with Cohen's d < 0.20 in different severities of dementia on two indices and five subtests. The ICC values of these indices and subtests were 0.82-0.85 and 0.57-1.00, respectively. The other two indices (i.e., auditory memory and immediate memory) and two subtests (i.e., logical memory delayed recall and visual reproduction immediate recall) demonstrated small to moderate practice effect (d = 0.46-0.74) for people with mild severity of dementia.

On the whole, the WMS-IV has no to moderate practice effects and moderate to excellent test-retest reliability in people with dementia. The values of the RCIp with 95% confidence interval for the indices and subtests were provided in this study, which are useful to clinicians and researchers for interpreting the real score change in persons with dementia. The two indices (i.e., auditory memory and immediate memory) and two subtests (i.e., logical memory delayed recall and visual reproduction immediate recall) with noticeable practice effect should be used with caution when assessing memory function repeatedly in people with mild severity of dementia.