An observational study is a type of study where the researcher can observe but does not administer any treatment. Therefore, whatever would normally happen, the researcher has to allow it to happen.
Researchers can't change anything about the people or subjects they are studying. The researcher can record the variables of interest, but again, can't affect the study. People have to be allowed to do whatever it is they were going to do without interruption.
There are two types of observational studies:
EXAMPLEConsider observing people who are sick--those are called the cases--versus people that aren't sick, which are the controls. Then, you look back to see what similarities the cases have in common and what similarities the controls have in common.
EXAMPLEIndividuals are engaging in activities like smoking or jogging. You record what happens as it happens, as opposed to trying to look back and figure it out.
That inspired some new studies, one of which began in 1934. It dealt with several thousand doctors, so it was a physician’s smoking study. The reason doctors were chosen is that doctors are usually very diligent about following protocols, meaning that those who smoked would likely continue to smoke, and those who didn't smoke would likely continue not smoking. Also, doctors typically wouldn't drop out of a study. Notice in the image below, how some of these physicians smoked, and some of them did not.
They did the study, and some of the doctors got cancer. Now, not every doctor who smoked ended up getting cancer, and not every person who got cancer was a smoker. However, what they found was that the vast majority of the time, it was the doctors who smoked that got cancer.
This study was conducted over a long period of time--a 20-year study. At its conclusion, this was the most convincing evidence that smoking had an effect on cancer. This was an example of a prospective study because it started with the doctors and followed them through to 1954.
It is important to note, however, that neither of these types of studies, prospective or a retrospective, can actually prove a cause-and-effect relationship. The only thing that can prove a cause-and-effect relationship between two variables is an experiment.
An experiment is a different type of study than an observational study. The differences will be covered in detail shortly, but essentially, the researchers are allowed to impose treatments on the participants. Treatments are administered and response to those treatments is measured. Because the researchers are the ones implementing the treatments and measuring the response, a cause-and-effect relationship between variables can be determined.
When discussing experiments, there is some very common terminology that you should be aware of. For example, as mentioned in the section above, subjects and participants are used interchangeably and describe people involved in an experiment. If animals or things are used in an experiment, they are referred to as experimental units. While it may seem a bit impersonal, it is universal terminology in the field of experiments.
In an observational study, the researcher observes the individuals but does not administer treatment. The researcher simply has to allow what would normally happen to happen. Again, they can record variables of interest, but not affect it in any way. The researcher is not necessarily an active participant in the study, other than observing and recording.
An experiment, on the other hand, is far more active on the part of the researcher. The researcher is creating the differences between the two groups, then determining whether or not there is a cause-and-effect relationship.
If you have a study that you'd like to do, but you can't perform it due to ethical or practical concerns, or it takes too much time or money, you can avoid those concerns or circumvent them by doing an observational study.