Prospective controlled trial definition

Try out PMC Labs and tell us what you think. Learn More. Randomized controlled trials RCT are prospective studies that measure the effectiveness of a new intervention or treatment. Although no study is likely on its own to prove causality, randomization reduces bias and provides a rigorous tool to examine cause-effect relationships between an intervention and outcome.

This is because the act of randomization balances participant characteristics both observed and unobserved between the groups allowing attribution of any differences in outcome to the study intervention. This is not possible with any other study design. In designing an RCT, researchers must carefully select the population, the interventions to be compared and the outcomes of interest. Once these are defined, the number of participants needed to reliably determine if such a relationship exists is calculated power calculation.

Participants are then recruited and randomly assigned to either the intervention or the comparator group. This is often ensured by using automated randomization systems e. RCTs are often blinded so that participants and doctors, nurses or researchers do not know what treatment each participant is receiving, further minimizing bias.

Key Concept: The distinguishing feature of a prospective cohort study is that at the time that the investigators begin enrolling subjects and collecting baseline exposure information, none of the subjects has developed any of the outcomes of interest.

Examples of Prospective Cohort Studies. Pitfall: Note that in these prospective cohort studies a comparison of incidence between the groups can only take place after enough time has elapsed so that some subjects developed the outcomes of interest. Since the data analysis occurs after some outcomes have occurred, some students mistakenly would call this a retrospective study, but this is incorrect.

The analysis always occurs after a certain number of events have taken place. The characteristic that distinguishes a study as prospective is that the subjects were enrolled, and baseline data was collected before any subjects developed an outcome of interest.

In contrast, retrospective studies are conceived after some people have already developed the outcomes of interest. The investigators jump back in time to identify a cohort of individuals at a point in time before they have developed the outcomes of interest, and they try to establish their exposure status at that point in time. They then determine whether the subject subsequently developed the outcome of interest.

Suppose investigators wanted to test the hypothesis that working with the chemicals involved in tire manufacturing increases the risk of death. Typically, one might consider finding an occupational setting in which there were large numbers of subjects with the exposure of interest. The survivors of the atomic bomb blasts in Japan at the second world war would also be considered a special exposure cohort. The employees who actually worked with chemicals used in the manufacturing process would be the exposed group, while clerical workers and management might constitute the "unexposed" group.

However, rather than following these subjects for decades, it would be more efficient to use employee health and employment records over the past two or three decades as a source of data.

In essence, the investigators are jumping back in time to identify the study cohort at a point in time before the outcome of interest death occurred. They can classify them as "exposed" or "unexposed" based on their employment records, and they can use a number of sources to determine subsequent outcome status, such as death e. Key Concept: The distinguishing feature of a retrospective cohort study is that the investigators conceive the study and begin identifying and enrolling subjects after outcomes have already occurred.

Open topic with navigation. A prospective study watches for outcomes, such as the development of a disease, during the study period and relates this to other factors such as suspected risk or protection factor s. The study usually involves taking a cohort of subjects and watching them over a long period. The outcome of interest should be common; otherwise, the number of outcomes observed will be too small to be statistically meaningful indistinguishable from those that may have arisen by chance.

All efforts should be made to avoid sources of bias such as the loss of individuals to follow up during the study. Prospective studies usually have fewer potential sources of bias and confounding than retrospective studies. A retrospective study looks backwards and examines exposures to suspected risk or protection factors in relation to an outcome that is established at the start of the study. Many valuable case-control studies, such as Lane and Claypon's investigation of risk factors for breast cancer, were retrospective investigations.