Are your p-values valid? The Shapiro-Wilk test is the "gold standard" for checking normality in biomedical research. This guide breaks down exactly how to perform the test in GraphPad Prism, SPSS, and R, how to interpret the results (p < 0.05 vs p > 0.05), and what to do when your data "fails" the test. Don't risk a rejected manuscript—master your statistical assumptions today.