The word treatment appears many times in the typical text on statistics and/or research design. It appears frequently in the indices of such texts. It is rarely defined. It is defined here, and how the term is used by researchers is shown.
Treatments, Treatment Effects, Independent Variables, and Experimental Research
Researchers are most likely to use the word treatment when referring to experimental research, especially when the data from that research were analyzed via analysis of variance (ANOVA). In experimental research, the researcher manipulates the independent or treatment variable(s) and then observes whether the treatment groups differ on one or more dependent or outcome variables.
In multiple-case research, the scores of two or more groups of cases (which might be the same research units or might be ...