5.8: Types of Research Studies - Experimental Studies
Experimental research includes interventions and randomized controlled trials or clinical trials. When researchers are testing whether or not a particular health program works, or a particular drug is effective, they use these types of experimental studies. The hallmark of an experimental study is that the researchers are testing a certain metric before and after the intervention to determine whether or not their experimental protocol or drug caused a specific outcome. Studies like these often have three steps: a pre- test, the experimental protocol, and then a post- test.
Interventions are often done to test a drug, medical technique, or health program and see if it can lead to a positive health outcome. Let’s take a common public health behavioral intervention like exercise, with a goal of improving a health outcome like reducing blood pressure. In this example perhaps we wanted to find out if offering a free exercise program in a particular community would decrease blood pressure readings in participants. We would test the participants blood pressure before offering the exercise program, offer the exercise program for a number of weeks, and then test blood pressure again at the end of the program. Some of these types of intervention studies are done simply to see if that program is feasible for the community. If it’s the very first time an intervention is implemented in a specific community, they might start with a smaller group to test for feasibility. This is called a pilot study. Some interventions and pilot studies have control groups as well. For our example, including a control group might require testing blood pressure in subjects in another neighborhood that did not have the exercise intervention. Control groups are a hallmark of well-conducted interventions, because they compare the experiment to a similar situation without the experiment. How do researchers know that the outcome wouldn’t have happened anyway without their experimental intervention? The control group provides that comparison.
Randomized controlled trials (RCTs) are a type of experimental study/intervention which is considered the highest level of research in determining cause and effect. This is for several reasons. First, by randomizing the selection of subjects, this removes selection bias and assumes that the subject pool (experimental group and control group) will be as similar to each other and the general population as possible. Second, RCTS have a control group, or perhaps a placebo group. Third, a controlled trial attempts to “control” the study for as many potentially confounding variables as possible. To some extent, this can be done after the fact via statistical calculations, but this can also sometimes be done in the study design. Let’s say for example we were measuring weight loss with our exercise intervention. What else could cause weight loss in either our experimental or control subjects? If several of them went on a diet, or started taking weight-loss medications, or did extra exercise outside of the program, these factors could “confound” our results - i.e. their weight changes would be a result of these other things, not the exercise program itself. As the researchers, we would therefore have to take steps in designing the study in order to reduce these confounding factors (such as asking participants not to change their diet or requiring that subjects are not on weight-loss medication in order to be a part of the study). Additionally, many RCTs are blinded or double-blinded, where the participants and/or the researchers are unaware of which participants are in the experimental and control groups. This helps to eliminate researcher bias (as the researchers might unknowingly treat the experimental participants differently), and it also helps to account for the placebo effect. The placebo effect is a real - not imagined - phenomenon of thinking one is taking some sort of treatment for a disease, and actually experiencing a positive outcome (Harvard Health Publishing, 2021). Using a placebo for the control group allows for the possibility of positive psychological effects from receiving treatment to be experienced by both groups. Thus, any additional improvement experienced by the experimental group could be attributed to the treatment itself, not a placebo effect. See Fig. \(\PageIndex{1}\) for a diagram of randomized controlled trials.