standard deviation below the mean respectively). In our categorical case we would use a simple regression equation for each group to investigate the simple slopes. It is common practice to standardize or center variables to make the data more interpretable in simple slopes analysis; however, categorical variables should never be standardized or centered. This test can be used with all coding systems. See also Level of measurement List of analyses of categorical data Qualitative data Statistical data type One hot encoding References Further reading Andersen, Erling B. 1980. Discrete Statistical Models with Social Science Applications. North Holland, 1980. Friendly, Michael. Visualizing categorical data. SAS Institute, 2000. NIST/SEMATEK (2008) Handbook of Statistical Methods Statistical data types Categorical data