Univariate comparisons given aggregated normative data

Normative comparison is a method to compare an individual to a norm group. It is commonly used in neuropsychological assessment to determine if a patient's cognitive capacities deviate from those of a healthy population. Neuropsychological assessment often involves multiple testing, which might increase the familywise error rate (FWER). Recently, several correction methods have been proposed to reduce the FWER. However these methods require that multivariate normative data are available, which is often not the case. We propose to obtain these data by merging the control group data of existing studies into an aggregated database. In this paper, we study how the correction methods fare given such an aggregated normative database.

In a simulation study mimicking the aggregated database situation, we compared applying no correction, the Bonferroni correction, a maximum distribution approach and a stepwise approach on their FWER and their power to detect genuine deviations.

If the aggregated database contained data on all neuropsychological tests, the stepwise approach outperformed the other methods with respect to the FWER and power. However, if data were missing, the Bonferroni correction produced the lowest FWER.

Overall, the stepwise approach appears to be the most suitable normative comparison method for use in neuropsychological assessment. When the norm data contained large amounts of missing data, the Bonferroni correction proved best. Advice of which method to use in different situations is provided.