Methodology Series Module 1: Cohort Studies
Maninder Singh Setia, Maninder Singh Setia
Abstract
Cohort design is a type of nonexperimental or observational study design. In a cohort study, the participants do not have the outcome of interest to begin with. They are selected based on the exposure status of the individual. They are then followed over time to evaluate for the occurrence of the outcome of interest. Some examples of cohort studies are (1) Framingham Cohort study, (2) Swiss HIV Cohort study, and (3) The Danish Cohort study of psoriasis and depression. These studies may be prospective, retrospective, or a combination of both of these types. Since at the time of entry into the cohort study, the individuals do not have outcome, the temporality between exposure and outcome is well defined in a cohort design. If the exposure is rare, then a cohort design is an efficient method to study the relation between exposure and outcomes. A retrospective cohort study can be completed fast and is relatively inexpensive compared with a prospective cohort study. Follow-up of the study participants is very important in a cohort study, and losses are an important source of bias in these types of studies. These studies are used to estimate the cumulative incidence and incidence rate. One of the main strengths of a cohort study is the longitudinal nature of the data. Some of the variables in the data will be time-varying and some may be time independent. Thus, advanced modeling techniques (such as fixed and random effects models) are useful in analysis of these studies.
Keywords: Cohort studies; limitations; strengths.
Figures
References
- Hennekens CH, Buring JE. 1st ed. Philadelphia, USA: Lippincott Williams & Wilkins; 1978. Epidemiology in Medicine.
- Egeberg A, Khalid U, Gislason GH, Mallbris L, Skov L, Hansen PR. Impact of depression on risk of myocardial infarction, stroke and cardiovascular death in patients with psoriasis: A Danish Nationwide Study. Acta Derm Venereol. 2015 DOI: 10.2340/00015555-2218.
- Framingham Heart Study. [Last accessed on 2015 Nov 14]. Available from: .
- Jensen P, Ahlehoff O, Egeberg A, Gislason G, Hansen PR, Skov L. Psoriasis and new-onset depression: A Danish Nationwide Cohort Study. Acta Derm Venereol. 2015 DOI: 10.2340/00015555-2183.
- Jewell N. Boca Raton, US: Chapman and Hall/CRC; 2004. Statistics for Epidemiology.
- Twisk JW. 2nd ed. Cambridge, UK: Cambridge University Press; 2013. Applied Longitudinal Data Analysis for Epidemiology.
- Keiser O, Taffé P, Zwahlen M, Battegay M, Bernasconi E, Weber R, et al. All cause mortality in the Swiss HIV Cohort Study from 1990 to 2001 in comparison with the Swiss population. AIDS. 2004;18:1835–43.
- Rothman KJ, Greenland S, Lash TL. 3rd ed. Philadelphia, USA: Lippincott Williams and Wilkins; 2008. Modern Epidemiology.
- Kleinbaum D, Kupper L, Morgenstern H. New York, US: John Wiley and Sons, Inc; 2001. Epidemiologic Research.
- Pigott TD. A review of methods for missing data. Educ Res Eval. 2001;7:353–83.
- Samet JM, Munoz A. Cohort Studies. Epidemiol Rev. 1998;20:1–136.
- Swiss HIV Cohort Study. Schoeni-Affolter F, Ledergerber B, Rickenbach M, Rudin C, Günthard HF, et al. Cohort profile: The Swiss HIV Cohort study. Int J Epidemiol. 2010;39:1179–89.
- Hulley SB, Cummings SR, Browner WS, Grady D, Hearst N, Newman TB. 2nd ed. Philadelphia, USA: Lippincot Williams and Wilkins; 2001. Designing Clinical Research.
- Swiss HIV Cohort Study. [Last accessed on 2015 Nov 14]. Available from:
- Szklo M, Nieto FJ. Sudbury, MA: Jones and Bartlett Publishers, Inc; 2004. Epidemiology: Beyond the Basics.
- Snidjers TA, Bosker RJ. 2nd ed. London, UK: Sage Publications; 2012. Multilevel Analysis: An Introduction to Basic and Advanced Multilevel Modeling.
Source: PubMed