Chapter 49 - Nonrandomized controlled trials

Abstract

Experimental studies can be divided into two broad categories: true experimental and quasi-experimental studies. An archetypical example of a true experimental study design is randomized controlled trials (RCTs), where participants are assigned to one of the comparison groups (e.g., either control or treatment group) randomly. Randomization yields comparison groups with minimal selection bias, enhancing the ability to assess the causal relationship between the intervention and the outcome. Although considered the gold standard for clinical research, RCTs are not always possible due to logistic and ethical concerns. Hence, nonrandomized controlled trials (NCTs)—a quasi-experimental study design that does not utilize random assignment—can be good alternatives when RCTs are not feasible. It should be noted that NCTs can also fall under prospective studies in addition to experimental studies. This chapter will focus on NCTs including basic principles, strengths and weaknesses, and applicability in interventional radiology research.