Our recommendations are based in evidence. This means that when we look at a topic we look for an intervention or process that works and that does more good than harm. Most often, we do this by looking at published, peer-reviewed evidence or at systematic reviews that summarize existing published, peer-reviewed evidence. However, before we make any conclusions we see we need to understand the differences between types of research studies.

Research isn’t perfect and people or populations are not all the same. This makes it especially important to understand the strengths and weaknesses of different types of studies and to understand who was included in a study. Women and people of color were often not included in research studies and this is a barrier to making sure that everyone is getting the best care possible. There is a lot that we don’t know.

Of course, we also can’t and don’t do research on everything. See Parachute use to prevent death and major trauma related to gravitational challenge: systematic review of randomised controlled trials and the takeaway: you do have to use common sense.

Here are the most common types of studies you will see (and there is of course much nuance within these trials that is not included, but this is a fair overview):

  • – Randomized controlled trial. In general, this type of study is best when you are trying to figure out if there is a relationship between an intervention and a result or outcome. People are divided by chance (randomized) into two or more groups. Then, one group is given an intervention, like a drug, and the other group or groups is given a different intervention, a placebo (fake drug or intervention), or nothing at all. Randomization helps take away the effect of another characteristic or factor (like age) influencing results, but of course randomization isn’t perfect and you have to use common sense (see above). Also, in many cases, you cannot randomize a group of people to an intervention that you know will cause harm, like not wearing a parachute or not wearing sunscreen due to ethical reasons.
  • – Cohort study. This observational type of study looks at the differences in results of two or more groups of people who have been exposed to an intervention, like wearing sunscreen. Here, you are not deciding who is given what, instead the people themselves have already made this choice. In a cohort study, you can either plan on looking at the groups of people forward in time or you may look back in time. Generally, these types of studies are not as good at trying to figure out if there is a relationship because the people have chosen whether to be exposed and there may be some other factor causing the result, like age.
  • – Case control studies. This is another observational type of study that looks at differences between two or more groups of people. Here, you start with the outcome, in many cases a disease, like skin cancer. Generally, you want to make sure your groups are as similar as possible in terms of age, sex, etc then will then look back in time to see if there are differences between the group that has skin cancer and the group that does not (your case vs your control). One group may have had more exposure to the sun. Like a cohort study, in general, these types of studies may have some other factor causing a result, like age.
  • – Qualitative study. This type of study involves talking to people and analyzing what they tell you instead of looking at numbers.
  • – Systematic review. A systematic review is typically the best source for making a conclusion because this type of study is a summary of multiple other studies. This is what I look at most often when looking for evidence for a specific health care topic.


Finally, why does it matter that a study or summary of multiple studies be peer reviewed? The process allows experts to look at the process of how you did your research, ask questions that you might not have thought of, add context, point out flaws, and help make sure that the study is helping us to better understand the truth.

Unfortunately, facts and data aren’t enough to convince everyone. I think medical research and science in generally should do a better job at being more transparent and more accessible. We all deserve to better understand our world. This is why it is important to understand how to ask and answer questions. And whatever type of research you read or do, I strongly encourage you to wear sunscreen.

Ginny Weir, MPH
Director, Bree Collaborative