For between-cases independent variables, each case is in one and only one group. Each group has different cases. Groups defined by the characteristics of the cases, such as sex or ethnicity, are necessarily between.
For within-cases groups, each case is in both groups. Each group has the same cases. Examples include longitudinal data at several different time points and repeated measures of the dependent variable. When cases from each group are different but closely linked, the variable is treated as within-cases. Examples include data from both members of a family or test ingots molded at the same time.
One of the independent variables is between-cases and the other is within-cases.
© 2002, Gary McClelland