Study design

A Study design is a way to set up an epidemiological investigation, as a form of clinical trial.

Types of design
Some of the most popular designs are sorted below, with the ones at the top being the most powerful at reducing Observer-expectancy effect (but also most expensive, and in some cases introducing ethical concerns) and the ones at the bottom being the most affordable. Frequently the ones at the bottom are used earlier in the research cycle, to develop strong hypotheses worth testing with the more expensive research approaches.

Experimental

 * Randomized controlled trial
 * Double-blind
 * Single-blinded
 * Nonblinded
 * Nonrandomized controlled trial

Nonexperimental

 * cohort study
 * Prospective cohort
 * Retrospective cohot
 * Nested cohort
 * Case-control (Case series)
 * nested case-control study

Other terms

 * A "retrospective study" looks at past behavior, while a "prospective study" looks at future behavior.
 * "Equivalence trials" are designed to demonstrate that one treatment is as effective as another, while "superiority trials" are designed to demonstrate that one treatment is more effective than another.
 * When using "parallel groups", each patient receives one treatment; in a "cross-over study", each patient receives every treatment.
 * A longitudinal study studies a few subjects for a long period of time, while a cross-sectional study involves many subjects measured at once.