In a case-control study, the participants are selected base on
the outcome status
In a cohort study, the participants are selected based on
exposure status
A quasi-experiment is just an empirical study as there is no
systematic arrangement of selection of participants.
In a cross-sectional study, the participants are selected based
on inclusion and exclusion. It is mainly used in population-based
surveys so as to access the prevalence of the disease. As here
there is a study on both outcome and exposure status. Hence in
National surveys, it is used.