The typical ANOVA design, in which the populations studied are (or are treated as) fixed categorical variables - users of Drugs A, B, and C, for example. The independent variables and their levels are determined (fixed) by the researcher. Also called "Model I ANOVA."
Vogt, W. P. (2005). Dictionary of statistics & methodology: A nontechnical guide for the social sciences (3rd edition).Sage Publications. https://dx.doi.org/10.4135/9781412983907