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Research Guides@Tufts

Study Designs in the Health Sciences

An introduction to the main features and uses of study designs popular and unique to medicine and the health sciences.

Prospective Cohort Study

What is a prospective cohort study?

"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" [1].

"Major disadvantages for conducting a prospective cohort study include lengthy time of study, large sample sizes required to detect associations with rare cancer outcomes, the higher costs associated with subject recruitment and measurement over time, and specialized composition of cohorts that limit generalizability."[2]

Why use this type of study?

  •  "to investigate causes of diseases, particularly if the more rigorous methodology of randomized controlled trial (RCT) is unethical or not feasible" [3]
  • "to test hypotheses about prognosis or etiology"[3]
  • "to establish incidence rates for specific outcomes or diseases" [3]

References

  1. Boston University School of Public Health. Prospective and Retrospective Cohort Studies. https://sphweb.bumc.bu.edu/otlt/mph-modules/ep/ep713_analyticoverview/ep713_analyticoverview3.html. Access November 6, 2024

  2. Carpenter CL. CHAPTER 19 - Dietary Assessment. In: Heber D, editor. Nutritional Oncology (Second Edition) [Internet]. Burlington: Academic Press; 2006 [cited 2024 Nov 6]. p. 367–75. Available from: https://www.sciencedirect.com/science/article/pii/B9780120883936500750

  3. De Rango P. Prospective Cohort Studies. Eur J Vasc Endovasc Surg. 2016 Jan;51(1):151. doi: 10.1016/j.ejvs.2015.09.021. Epub 2015 Nov 1. 

Example

Dietary Approaches to Stop Hypertension (DASH) and mortality risk among patients with liver cirrhosis: a prospective cohort study. 

Zarei, A., Pashayee-Khamene, F., Hekmatdoost, A., Karimi, S., Ahmadzadeh, S., Saberifiroozi, M., Hatami, B., & Yari, Z.

BMC research notes, 17(1), 248. https://doi.org/10.1186/s13104-024-06928-z

Background and purpose: The relationship between dietary patterns and cirrhosis is undeniable. The present study aimed to investigate the association between the Dietary Approaches to Stop Hypertension (DASH) diet and the risk of mortality in patients with cirrhosis prospectively.

Methods: In this cohort study, 121 cirrhotic patients were enrolled and followed up annually for four years. Nutritional status and dietary intakes were assessed initially, and the DASH score was calculated accordingly. Crude and multivariable-adjusted hazard ratios (HR) with 95% confidence intervals (CI) were estimated using Cox proportional hazard analyses.

Results: DASH components including fruits, vegetables, legumes, nuts and seeds, and low-fat dairy products were significantly associated with lower mortality risk in cirrhotic patients. Also, a higher DASH score was significantly associated with a reduction in the risk of mortality in patients with cirrhosis, so that after adjusting for all confounders, the risk of mortality in the upper tertile was 89% lower than the first tertile (HR = 0.11, 95% CI: 0.03-0.42, P trend < 0.001). The 4-year survival rate among patients across tertiles of DASH was 32%, 37%, and 46%, respectively (P = 0.005).

Conclusion: It can be concluded that a higher DASH diet score may be associated with a reduced risk of mortality in cirrhotic patients. However, larger studies are needed to confirm the findings and determine their potential mechanisms.