Chance Performance and Floor Effects: Threats to the Validity of the Wechsler Memory Scale--Fourth Edition Designs Subtest

The Designs subtest allows for accumulation of raw score points by chance alone, creating the potential for artificially inflated performances, especially in older patients. A random number generator was used to simulate the random selection and placement of cards by 100 test naive participants, resulting in a mean raw score of 36.26 (SD = 3.86). This resulted in relatively high-scaled scores in the 45-54, 55-64, and 65-69 age groups on Designs II. In the latter age group, in particular, the mean simulated performance resulted in a scaled score of 7, with scores 1 SD below and above the performance mean translating to scaled scores of 5 and 8, respectively. The findings indicate that clinicians should use caution when interpreting Designs II performance in these age groups, as our simulations demonstrated that low average to average range scores occur frequently when patients are relying solely on chance performance.