BACKGROUND: The traditional Bonferroni method is a commonly used post hoc hypothesis test to adjust for familywise error rate inflation; however, a less well-known derivative of this test, the Holm's sequential procedure, provides an alternative method for familywise error rate correction. This less conservative approach is particularly relevant to studies investigating neuropsychological functioning because of the extent to which neuropsychological datasets tend to include interrelated outcome measures, reducing the relevance of the universal null hypothesis assumption, on which the traditional Bonferroni method relies. METHODS: Mathematical illustrations demonstrating how to compute the two adjustments are provided. The two methods are compared using a simple hypothetical dataset. RESULTS: By using the divisors (n − j + 1) in lieu of n, Holm's sequential procedure is guaranteed to never reject fewer hypotheses than the traditional Bonferroni adjustment. CONCLUSIONS: The Holm's sequential procedure corrects for Type I error as effectively as the traditional Bonferroni method while retaining more statistical power. Although the Holm's sequential procedure is more complicated to compute than the traditional Bonferroni method, the Holm's sequential procedure may be a more appropriate method for adjusting familywise error rate inflation in many types of neuropsychological research.

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Persons who have the genetic mutation responsible for Huntington's disease (HD) have been shown to exhibit lower cognitive test scores years prior to manifest HD. Most studies have examined cognitive performance in presymptomatic persons by using estimated times to manifest HD based on published algorithms. We followed 19 gene-positive persons who were presymptomatic using an objective criterion (i.e., Quantified Neurological Exam score ≤ 10) at baseline for up to 21 years (median = 5 years) with periannual neuropsychological assessments until a diagnosis of manifest HD. Results showed that our tests of information- and psychomotor-processing speed that place minimal demands on cognition, worsening performance became evident 5-10 years prior to the development of manifest HD. In conclusion, cognitive decline precedes motor signs in HD and may be an important target in clinical trials and early intervention. Cognitive test scores may also improve the ability to predict disease onset among gene mutation carriers and help families to better plan for potential personal and economic hardship.