3. Types of epidemiological studies

3.2 Analytic studies

3.2.2 Intervention studies

B. Quasi- experimental studies

These are set up when randomization of the time and duration of exposure of the subjects in the experimental study is impossible.

In these studies, a therapy or an intervention is applied to a selected group of individuals. This group is compared to a control group that has not received the intervention. The efficacy of the intervention is then determined.

The difference with experimental studies is that the subjects are not selected randomly. The investigator selects the individuals who will receive the intervention.

Example: This can be an intervention for improving influenza vaccination coverage among health care workers in a hospital. The investigator chooses a department where a vaccination campaign will be set up (treatment center). After the study, vaccine coverage at this center is compared to a control center that did not receive the intervention.