The research method is the same as that of the continuous data. There are equivalent designs with continuous data. Only difference is the characteristic of the data, which is categorical data. The researcher plans to measure the response variable depending on the explanatory variable. The most important factor in the experimental design is randominization.
Clinical trial is one example of the categorical experimental design.
Although the researcher plans to measure the response variable depending on the explanatory variable, there is a lack of randominization in the quasi-experimental design. The observational study may be either prospective or retrospective design. If the researcher begins to observe, waiting for the results, it is a prospective design. If she gathers data at one time and traces the difference into the past, it is a retrospective design. Relationships Among Research Designs 2.