What type of study is described when researchers randomly assign participants to receive a treatment or placebo and then track outcomes over time?

The described study is an experimental study because it involves researchers actively manipulating one variable to observe its effect on another. In this case, participants are randomly assigned to either a treatment group or a placebo group, allowing for a controlled comparison of outcomes. This random assignment helps eliminate biases and confounding variables, thereby improving the internal validity of the results. The focus is on determining causal relationships between the treatment and the outcomes, which is a hallmark of experimental designs.

While observational studies observe subjects in their natural settings without manipulation, case studies focus on an in-depth analysis of a single subject or group without random assignment. Longitudinal studies track data over an extended period but do not necessarily involve random assignment or treatment interventions; thus, they may lack the same level of control as experimental studies. Therefore, the defining characteristic of this type of study is the random assignment of participants to different groups to evaluate the effect of a specific treatment.