Apparently abnormal Wechsler Memory Scale index score patterns in the normal population

Area of Science:

• Neuropsychological assessment
• Psychometrics
• Cognitive psychology

Background:

• Interpreting Wechsler Memory Scale-Fourth Edition (WMS-IV) scores often involves comparing index scores.
• Previous data suggested 15-point differences between index scores were uncommon in healthy individuals.
• However, these base rates did not account for multiple simultaneous comparisons.

Purpose of the Study:

• To provide normative data on the frequency of multiple index score differences in the Wechsler Memory Scale-Fourth Edition (WMS-IV).
• To assess the clinical meaningfulness of score discrepancies when numerous comparisons are made.
• To validate findings using Monte Carlo simulations against standardization data.

Main Methods:

• Utilized Monte Carlo simulations to generate normative data for multiple index score differences.
• Validated simulation results against existing standardization sample data for the WMS-IV and Wechsler Adult Intelligence Scale-Fourth Edition (WAIS-IV).
• Calculated the occurrence of 15-point differences between memory indexes and between memory and ability indexes.

Main Results:

• Differences of 15 points between any two WMS-IV memory indexes occurred in 60% of the normative sample.
• Differences of 15 points between WMS-IV memory indexes and Wechsler Adult Intelligence Scale-Fourth Edition (WAIS-IV) ability indexes occurred in 48% of the sample.
• Monte Carlo simulations accurately predicted these observed false-positive rates.

Conclusions:

• Wechsler index score discrepancies of 15 points are common in the normative sample.
• These discrepancies are likely not clinically meaningful when multiple comparisons are performed.
• Explicit interpretive hypotheses are crucial to reduce false-positive conclusions in WMS-IV interpretation.