Overview Interventional studies are prospective studies designed to evaluate the direct impact of therapies or preventative measures by assigning subjects to intervention groups 2 types of interventional studies clinical trials individuals assigned to competing intervention groups community interventions assigment at the group level (e.g. one community receives fluoridinated water and one does not) Highest quality if randomized controlled double-blinded Clinical Drug Trials 4 phases for clinical trials evaluating new drugs phase I small number of healthy subjects (< 100) purpose safety and dosage phase II small number of diseased patients (100-300) purpose efficacy and side effects phase III large number of diseased patients (> 1,000) purpose effectiveness and monitoring of adverse reactionscompare to standard of care phase IV post-marketing surveillance purpose detects rare or long-term adverse effects Factorial Design Randomizes patients into different interventions with 2 or more variables being studied in each intervention allows researchers to study the effects of multiple independent variables independently and mutually on a dependent variable e.g., group 1 studies effect of treatments A+B on variable X, group 2 studies effects of A alone, group 3 studies effect of B alone, and group 4 is the control group receiving no treatment Crossover design Participants alternate receiving intervention and placebo Participants act as own controls improves power and precision of study need washout period between interventions all patients receive intervention