Introduction to Observational Studies
1.1 Observational vs. Experimental Studies
When a researcher designs and performs an experimental study, the assignment of exposure (or treatment)* is under the researcher’s control and is done randomly. Random assignment uses chance to form treatment groups that are expected to be comparable. Studies without this feature are collectively referred to as observational or non-experimental studies. In research involving human subjects, experimental studies are typically called randomized controlled trials (RCTs).