Guide to Understanding Clinical Research Studies

Clinical research involves the study of human participants and may be either:

1. Observational, where researchers observe and document people’s characteristics or behaviors and evaluate for associations with outcomes, or
2. Interventional, where researchers assign participants a particular intervention (treatment, procedure, or behavior change) to see how this affects outcomes. This is also called a ‘clinical trial.’

Clinical trials are generally recognized as providing stronger evidence than observational studies because observational studies show only an association but cannot determine that one thing definitively causes a change in an outcome.

There are several factors to be aware of in evaluating the strength and limitations of a study and the most relevant are outlined here.

For interventional clinical trials:

1. Sample size (or “n”): refers to the number of study participants. Generally, more study participants leads to greater confidence in the results.
2. Duration: longer studies provide more of an opportunity to show differences between groups and demonstrate long-term outcomes.
3. Presence of a control group: a control group is not exposed to the intervention under study. This produces more rigorous results because it allows for comparison of differences in outcomes between the intervention group and control group.
4. Randomization: randomly assigning participants to intervention and control groups helps to evenly distribute individual factors or choices unrelated to the intervention that could influence outcomes. This tends to reduce bias and create more robust results.
5. Blinding: refers to whether participants and study investigators who record outcomes are aware of which group (intervention or control) the participants are in. Humans can be prone to unconscious behaviors based on what they know so the more blinding, the less potential for bias.
6. Adherence: the better participants adhere to the intervention, the more certain you can be about the results. Interventions that have better adherence may be easier for people to follow.

For observational studies:

1. Sample size (or “n”): refers to the number of study participants. Generally, more study participants leads to greater confidence in the results.
2. Time points: Cross-sectional studies provide only a “snapshot” in time. Longitudinal studies are generally recognized as stronger evidence because they show change over time.
3. Duration: longer studies provide more opportunity to show differences between groups and demonstrate long-term outcomes.
4. Type of measurement: objective measurements (such as blood pressure and body weight) are generally more reliable than subjective measurements (like pain and fatigue) that require people to remember and report their behaviors.