Nonrandomized interventional study designs (quasi-experimental designs)

In contrast to observational study designs, interventional studies manipulate clinical care to evaluate treatment effects on outcomes. Although surgeons have often relied on observational studies to establish the efficacy and effectiveness of operative and perioperative interventions, observational studies (also referred to as case series) are limited to demonstrating the correlation between the outcome of interest and the procedure. Prospective controlled interventional trials will provide a higher level of evidence for a true cause-and-effect relationship.