Research Design and Statistical Consulting

George M. Diekhoff, Ph.D.

When using the bar graphs that are generated by the Frequencies procedure in SPSS, if you’ve told SPSS to represent percentages on the vertical axis you need to be aware that your category bars will indicate the percentage of those who responded to the item that fall into each category of the variable. In other words, these are “valid percentages,” not “percentages.” The bar graphs generated by the Frequencies procedure do not give you the option of plotting “percentages,” i.e., the percentage of the whole sample, those who responded and those who didn’t,that fall into each category. To plot percentages of the whole sample in each category, including the “missing” or “nonresponding” category, click on Graphs (in the menu bar) > Legacy Dialogs > Bar > Simple (for most situations) > Define > Options, then in the Missing Values area, check “Display groups defined by missing values.” The resulting bar graph will indicate percentages of the whole sample fall into each category of variable, including the missing values category.