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.
The participants in a prospective study are selected based on specific criteria and are often free from the outcome of interest at the beginning of the study. Data on exposures and potential confounding factors are collected at regular intervals throughout the study period.
By following the participants prospectively, researchers can establish a temporal relationship between exposures and outcomes, providing valuable insights into the causality of the observed associations.
This study design allows for the examination of multiple outcomes and the investigation of various exposure levels, contributing to a comprehensive understanding of the factors influencing health and disease.
How it Works
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 is investigated, medical professionals will identify a cohort, observe the target participants over time, and collect data at regular intervals.
Weeks, months, or years later, depending on the duration of the study design, the researchers will 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 study 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 can also reveal links between 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 can identify a disease’s causes 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.
Examples
- Framingham Heart Study: Studied the effects of diet, exercise, and medications on the development of hypertensive or arteriosclerotic cardiovascular disease in 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
1. What does it mean when an observational study is prospective?
A prospective observational study is a type of research where investigators select a group of subjects and observe them over a certain period.
The researchers collect data on the subjects’ exposure to certain risk factors or interventions and then track the outcomes. This type of study is often used to study the effects of suspected risk factors that cannot be controlled experimentally.
2. What is the primary difference between a randomized clinical trial and a prospective cohort study?
In a retrospective study, the subjects have already experienced the outcome of interest or developed the disease before the start of the study.
The researchers then look back in time to identify a cohort of subjects before they had developed the disease and use existing data, such as medical records, to discover any patterns.
In a prospective study, on the other hand, the investigators will design the study, recruit subjects, and collect baseline data on all subjects before any of them have developed the outcomes of interest.
The subjects are followed and observed over a period of time to gather information and record the development of outcomes.
3. What is the primary difference between a randomized clinical trial and a prospective cohort study?
In randomized clinical trials, the researchers control the experiment, whereas prospective cohort studies are purely observational, so researchers will observe subjects without manipulating any variables or interfering with their environment.
Researchers in randomized clinical trials will randomly divide participants into groups, either an experimental group or a control group.
However, in prospective cohort studies, researchers will identify a cohort and observe the target participants as a whole to examine any factors that differ between the individuals who develop the condition and those who do not.
References
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. de_mutsert@ 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.
Further Information
- Euser, A. M., Zoccali, C., Jager, K. J., & Dekker, F. W. (2009). Cohort studies: prospective versus retrospective. Nephron Clinical Practice, 113(3), c214-c217.
- Design of Prospective Studies
- Hammoudeh, S., Gadelhaq, W., & Janahi, I. (2018). Prospective cohort studies in medical research (pp. 11-28). IntechOpen.
- Nabi, H., Kivimaki, M., De Vogli, R., Marmot, M. G., & Singh-Manoux, A. (2008). Positive and negative affect and risk of coronary heart disease: Whitehall II prospective cohort study. Bmj, 337.
- Bramsen, I., Dirkzwager, A. J., & Van der Ploeg, H. M. (2000). Predeployment personality traits and exposure to trauma as predictors of posttraumatic stress symptoms: A prospective study of former peacekeepers. American Journal of Psychiatry, 157(7), 1115-1119.
