Quasi-experimental study designs, sometimes called nonrandomized, pre-post-intervention study designs, are ubiquitous in the infectious diseases literature, particularly in the area of interventions aimed at decreasing the spread of antibiotic-resistant bacteria. Little has been written about the benefits and limitations of the quasi-experimental approach. This article outlines a hierarchy of quasi-experimental study design that is applicable to infectious diseases studies and that, if applied, may lead to sounder research and more-convincing causal links between infectious diseases interventions and outcomes.