Table 1.

Definitions of Study Designs

Cross Sectional Study: A cross-sectional study is a descriptive study in which disease, risk factors, or other characteristics are measured simultaneously (at one particular point in time) in a given population (Last, 2001).

Cohort Study: A cohort study is an analytical study in which individuals with differing exposures to a suspected factor are identified and then observed for the occurrence of certain health effects over a period of time (Last, 2001). Comparison may be made with a control group, but interventions are not normally applied in cohort studies.

Case-Control: A case-control study is an analytical study which compares individuals who have a specific condition (“cases”) with a group of individuals without the condition (“controls”) (Last, 2001). A case-control study generally depends on the collection of retrospective data, thus introducing the possibility of recall bias. Recall bias is the tendency of subjects to report events in a manner that is different between the two groups studied.

Controlled Trial: A controlled trial is an experimental study comparing the intervention administered in one group of individuals (also referred as treatment, experimental or study group) and the outcome compared to a similar group (control group) that did not receive the intervention (Fowkes, 1991). A controlled trial may or may not use randomization to assign individuals to groups, and it may or may not use blinding to prevent them from knowing which treatment they get. In the event study participants are randomly assigned (meaning everyone has an equal chance of being selected) to a treatment or control group, this study design would be referred to as a randomized controlled trial.