Hi,
for standardizing a data set or (x-mean)/variance we are assuming a Gaussian distribution for the data. What should we do to know that this assumption is valid for our data? should we for example draw the QQ-Plot?
Thanks

Common approaches are Q-Q plots, testing the residuals (both group combined, mean calculated, each observation - mean = residual) with a normality test (e.g., Shapiro-Wilk), or sometimes central limit theory of large samples (sample > 30).