Type I and Type II Errors in Correlations of Various Sample Sizes1

This study documented the effect of sample sizes commonly seen in exercise science research on type I and type II errors in statistical tests of numerous correlations. Data on tennis string testing were used to examine zero-order and partial correlations between six variables for the population (N = 198) and three randomly drawn sub-samples of 99, 50, and 25. Sample size and statistical analysis procedure affected the rates of statistical errors. Reducing sample size increased type II errors 7% to 21% using correlation analysis. Partial correlation analysis of smaller samples increased type II errors 29% to 85%. Correlation studies of small sample sizes are likely vulnerable to type I or type II statistical errors and should be interpreted with caution.