title: Multiple correlations and Bonferroni's correction.
abstract: Correlation coefficients between biological measurements and clinical scales are often calculated in psychiatric research. Calculating numerous correlations increases the risk of a type I error, i.e., to erroneously conclude the presence of a significant correlation. To avoid this, the level of statistical significance of correlation coefficients should be adjusted. Threshold levels of significance for correlation coefficients were adjusted for multiple comparisons in a set of k correlation coefficients (k = 1, 5, 10, 20, 50, 100) by Bonferroni's correction. Significant correlation coefficients were then calculated according to sample size. The change in the threshold values of significance is larger when the number of correlations goes from 1 to 5 than when it goes from 50 to 100. A correlation coefficient, statistically significant at 5% when calculated alone, can be under the threshold level of significance when calculated even among a few other coefficients. Focusing on the most relevant variables or the use of multivariate statistics is advocated.
authors.affiliation: Department of Psychiatry, Geneva University, Switzerland.
authors.forename: F
authors.initials: F
authors.lastname: Curtin
authors.forename: P
authors.initials: P
authors.lastname: Schulz
mesh_terms: D003627:Data Interpretation, Statistical; D011569:Psychiatric Status Rating Scales; D011570:Psychiatry / Q000706:statistics & numerical data*; D012107:Research Design; D018401:Sample Size