What is the purpose of a Bonferroni correction?

The Bonferroni correction is used to adjust P values when multiple comparisons are made within a statistical analysis. When conducting multiple hypothesis tests, the chance of obtaining at least one significant result due to random chance increases. The Bonferroni correction addresses this issue by altering the threshold for significance—specifically, by dividing the desired alpha level (commonly set at 0.05) by the number of comparisons being made. This adjustment helps to maintain the overall type I error rate, ensuring that the likelihood of falsely rejecting a null hypothesis remains at a predetermined level. Hence, this method is essential for controlling the family-wise error rate and improving the interpretability of results in studies involving multiple tests.