A prospective study, loosely defined, is a study that starts in the present and continues forward in time. It is differentiated from a retrospective study, which looks at a known outcome backward, determining the factors that influenced the outcome. The retrospective study already has the material at hand, which can help make determinations about cause and effect, but the prospective researcher gathers information as an experiment or study progresses. This term is defined loosely because there are numerous permutations of both prospective and retrospective studies, and they can vary widely in how they are conducted.
Understanding the term "prospector" is useful when getting a sense of prospective studies. The prospector looks for things he hopes to find, like gold or oil. The researcher performs much the same task, by defining what she hopes to see and then testing the matter. Sometimes research is open to numerous prospects or it may be limited to simple questions like: “Does this drug or treatment work?”
Certainly, a common reason to perform a prospective study is to get information about how some type of treatment will work. For many drug experiments, scientists put together a cohort or a group people that have some similarities, such as all suffering from the same illness, all of the same gender, or all near the same age. Other cohorts are possible, depending on the interests of the researcher and goals of the study. It should be noted the terms "study" and "experiment" are often differentiated, with experiment applying specifically to research that uses some type of treatment.
In a prospective experiment, given a collected cohort, researchers then administer some treatment for a set period of time, carefully examining and recording the results of each individual. In drug experimentation, usually half of the subjects receive a placebo treatment so it can be determined if there is any true difference between those given the true drug and those who don’t receive it. The prospective experiment could take a few weeks, months or several years.
A true prospective study can last for years. Scientists might simply create a cohort and look to see if they develop certain things over time, without applying treatments. Keeping together a cohort can be challenging and as studies lengthen, people drop out, or the complexities of life choices make it difficult to determine results. Yet the results of a long-term prospective study can be fascinating, though it can be difficult, time-consuming and expensive.
Usually, if people want to evaluate outcomes, they look backward. For example, if a researcher wants to study the risk factors for lung cancer, she could compile information about patients who have died from it, and determine what factors each subject had in common with the others. This wouldn’t prove all causes of the cancer, but it could be a useful way to evaluate correlation. Drugs can also be studied retrospectively to determine if they’re having unwanted or additional beneficial effects that were previously unknown, but new drugs always require prospective study.