What is a Prospective Study?

By Julia Simkus, published Jan 19, 2022

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A prospective study, sometimes called a prospective cohort study, is a type of longitudinal study where researchers will follow and observe a group of subjects over a period of time to gather information and record the development of outcomes.

Participants are enrolled in the study before they develop the outcome or disease in question and then are observed as it evolves to see who develops the outcome and who does not.

Cohort studies are observational, so researchers will follow the subjects without manipulating any variables or interfering with their environment.

Similar to retrospective studies, prospective studies are beneficial for medical researchers, specifically in the field of epidemiology, as scientists can watch the development of a disease and compare the risk factors among subjects.

Before any appearance of the disease under investigation, medical professionals will identify a cohort, observe the target participants over time, and collect data at regular time intervals.

Weeks, months, or years later, depending on the duration of the study design, the researchers examine any factors that differed between the individuals who developed the condition and those who did not.

They can then determine if an association exists between an exposure and an outcome, and even identify disease progression and relative risk.

Advantages

Determine cause and effect relationships

Because researchers are studying groups of people before they develop an illness, they can discover potential cause and effect relationships between certain behaviors and the development of a disease.

Multiple diseases and conditions can be studied at the same time

Prospective cohort studies enable researchers to study causes of disease and identify multiple risk factors associated with a single exposure. These studies also can reveal links among different types of diseases and risk factors.

Can measure a continuously changing relationship between exposure and outcome

Because prospective cohort studies are longitudinal, researchers can study changes in levels of exposure over time and any changes in outcome, providing a deeper understanding of the dynamic relationship between exposure and outcome.

Limitations

Time consuming and expensive

Prospective studies usually require multiple months or years before researchers are able to identify causes of a disease or discover significant results.

Because of this, they are often more expensive than other types of studies. Recruiting and enrolling participants is another added cost and time commitment.

Requires large subject pool

Prospective cohort studies require large sample sizes in order for any relationships or patterns to be meaningful. Researchers are unable to generate results if there is not enough data.

Prone to bias

Because of the longitudinal nature of these studies, it is common for participants to drop out and not complete the study.

The loss of follow-up in prospective studies means researchers are more likely to incorrectly estimate the effects of an  

Examples

• Framingham Heart Study: Studied the effects of diet, exercise, and medications on the development of hypertensive or arteriosclerotic cardiovascular disease on residents of the city of Framingham, Massachusetts.
• Caerphilly Heart Disease Study: Examined relationships between a wide range of social, lifestyle, dietary and other factors with incident vascular disease.
• The Million Women Study: Analyzed data from more than one million women aged 50 and over to understand the effects of hormone replacement therapy use on women's health.
• Nurses’ Health Study: Studied the effects of diet, exercise, and medications on the development of hypertensive or arteriosclerotic cardiovascular disease.
• Sleep-Disordered Breathing and Mortality: Determined whether sleep-disordered breathing and its sequelae of intermittent hypoxemia and recurrent arousals are associated with mortality in a community sample of adults aged 40 years or older (Punjabi et al., 2009)

Frequently asked questions about prospective cohort studies

Sources

Euser, A. M., Zoccali, C., Jager, K. J., & Dekker, F. W. (2009). Cohort studies: prospective versus retrospective. Nephron. Clinical practice, 113(3), c214–c217. https://doi.org/10.1159/000235241

Hariton, E., & Locascio, J. J. (2018). Randomised controlled trials - the gold standard for effectiveness research: Study design: randomised controlled trials. BJOG : an international journal of obstetrics and gynaecology, 125(13), 1716. https://doi.org/10.1111/1471-0528.15199

Netherlands Cooperative Study on the Adequacy of Dialysis-2 Study Group de Mutsert Renée r. [email protected] lumc. nl Grootendorst Diana C Boeschoten Elisabeth W Brandts Hans van Manen Jeannette G Krediet Raymond T Dekker Friedo W. (2009). Subjective global assessment of nutritional status is strongly associated with mortality in chronic dialysis patients. The American journal of clinical nutrition, 89(3), 787-793.

Punjabi, N. M., Caffo, B. S., Goodwin, J. L., Gottlieb, D. J., Newman, A. B., O'Connor, G. T., Rapoport, D. M., Redline, S., Resnick, H. E., Robbins, J. A., Shahar, E., Unruh, M. L., & Samet, J. M. (2009). Sleep-disordered breathing and mortality: a prospective cohort study. PLoS medicine, 6(8), e1000132. https://doi.org/10.1371/journal.pmed.1000132

Ranganathan, P., & Aggarwal, R. (2018). Study designs: Part 1 - An overview and classification. Perspectives in clinical research, 9(4), 184–186.

Song, J. W., & Chung, K. C. (2010). Observational studies: cohort and case-control studies. Plastic and reconstructive surgery, 126(6), 2234–2242. https://doi.org/10.1097/PRS.0b013e3181f44abc.