Often the best test of a hypothesis since cause precedes effect. These are not typically seen in the anesthesiology literature. Unlike retrospective and prospective studies that are longitudinal in nature, cross-sectional studies allow for the ascertainment of cause and effect at the same point in time. In these types of studies there is a deliberate action on the part of the investigator to intervene or alter the course of the study. The most common type of experimental study is the randomized clinical trial, which are used to evaluate the effect of a new drug, procedure, or intervention on outcome.
Randomization maximizes the comparability of groups and reduces confounding.
A third type of study design typically seen in the anesthesiology literature is surveys. These deserve separate mention since they are governed by the science of psychometrics. Precision is determined by measurements of the reliability and validity of the questionnaire.