3.1 Three types of study designs

From the RQ, we know what data must be collected from the individuals in the study (the response and explanatory variables)… but how do we obtain this data? After all, data are important: they are the means by which the RQ is answered.

Three broad methods for obtaining data are to use:

  • Descriptive studies (Sect. 3.2), for answering Descriptive RQs;
  • Observational studies (Sect. 3.3), for answering Relational RQs; or
  • Experimental studies (Sect. 3.4), for answering Interventional RQs.

The type of study depends on the type of RQ.

Example 3.1 (Research design) Suppose we wish to compare the effects of echinacea on the symptoms of the common cold (based on Barrett et al. (2010)).

How would we design such a study to collect the necessary data? What decisions would you need to make?


Barrett B, Brown R, Rakel D, Mundt M, Bone K, Barlow S, et al. Echinacea for treating the common cold: A randomized trial. Annals of Internal Medicine. 2010;153(12):769–77.