Three commonly used study designs are described in this document:

1. Cross-Sectional Study
2. Cohort Study
3. Case-Control Study

1. Cross-Sectional Study

References: Oxford Centre for Evidence-Based Medicine; Lix, 2006; and Mann 2003

Cross-sectional study designs are used when studying one or more variables within a given population at one point in time. Such studies are useful for establishing associations rather than causality and for determining prevalence, rather than incidence.

Diagram from Mann 2003

Examples:

• MCHP study using a cross-sectional design: Kozyrskyj 2001

2. Cohort Study

References: Oxford Centre for Evidence-Based Medicine; and Lix, 2006

In cohort studies, a group of people within a population is followed over a specified period of time to track who experiences or develops the same significant life event or treatment. This type of design can be used "to study incidence, causes, and prognosis. Because they measure events in chronological order they can be used to distinguish between cause and effect." (Mann 2003) Cohort studies can be done prospectively, retrospectively, or using cross-sectional methods. As well, two groups may be followed: one containing the agent of interest and the other acting as a control group.

A sequential cohort study is an example of a cohort study which, instead of following a single age-homogeneous cohort, uses two or more distinct age cohorts and tracks each for a shorter period of time than in a regular cohort study. This convergence model combines cross-sectional and longitudinal data: there is a simultaneous model fitting of between- and within-individual trajectories over a wider span of time than observed longitudinal trends. This type of cohort study is efficient, potentially more representative (less longitudinal attrition), and reduces cumulative testing effects. However an (age x cohort) interaction may threaten validity of inferences  (Lix, 2006)

Diagram from Mann 2003

Examples:

• MCHP Studies using a cohort design: Menec 2004, Morgan 2003

3. Case-Control Study

References: Oxford Centre for Evidence-Based Medicine ; Mann 2003

Most commonly carried out retrospectively, case control studies are used to compare cases who have a certain condition with a control group known not to have developed the outcome of interest.The control group is usually not only taken from the same population base, but also matched for age and gender. Such studies "seek to identify possible predictors of outcome and are useful for studying rare disease or outcomes. They are often used to generate hypotheses that can then be studied via prospective cohort or other studies" (Mann 2003)

Family-based design is a specific type of retrospective case-control design. Related persons are used as the study control group, which "confers robustness against the potentially biasing effects of genetic admixture." Designs using sibling or cousins are "useful for diseases with early or later onset and can be analyed by using conditional logistic regression, with fine stratification on family." Designs using parents are useful for studies involving birth defects or diseases with early onsets. (Weinberg 2000)

Diagram from Mann 2003

Examples:

• MCHP Studies using a Case Control design: Kozyrskyj 2005, Cohen 1993

REFERENCES

• Brownell M, Lix L, Ekuma O, Derksen S, De Haney S, Bond R, Fransoo R, MacWilliam L, & Bodnarchuk J (2003). Why is the Health Status of Some Manitobans Not Improving? The Widening Gap in the Health Status of Manitobans. [Full Report (PDF)] [Summary (PDF)]
• Cohen MM. (1993) Using administrative data for case-control studies: The case of the papanicolaou smear. Ann Epidemiol 3(1):93-98
• Institute for Work and Health. Retrospective vs Prospective Studies. http://www.iwh.on.ca/at-work/59/retrospective-vs-prospective-studies accessed July 6, 2011.
• Jayawant N. Mandrekar, Sumithra J. Mandrekar.  An Introduction to Matching and Its Application Using the SAS® System (PDF) SUGI 29 Proceedings. Montreal, Canada: May 9-12 2004.
• Kozyrskyj A, Lix L, Dahl M, Soodeen R ( 2005). High-Cost Users of Pharmaceuticals: Who Are They? [Full Report (PDF)] [Summary (PDF)]
• Kozyrskyj A, Mustard C, Derksen S (2001). Studying Health and Health Care Use in At-Risk Groups.
• Lix L. Observational Epidemiology: Design and Analysis of Longitudinal Data. Lecture Notes. University of Manitoba. February 2006.
• Lori S. Parsons.  Performing a 1:N Case-Control Match on Propensity Score (PDF) SUGI 29 Proceedings. Montreal, Canada: May 9-12 2004.
• Mann CJ. Observational research methods. Research design II: cohort, cross sectional, and case-control studies. Emerg Med J 2003; 20:54-60 [Full Text]
• Mayo Foundation for Medical Education and Research. Locally Written SAS Macros (CFM) . http://mayoresearch.mayo.edu/mayo/research/biostat/sasmacros.cfm (CFM) Accessed February 6, 2006.
• Menec V, Lix L, Steinbach C, Okechukwu E, Sirski M, Dahl M & Soodeen RA (2004). Patterns of Health Care Use and Cost at the End of Life. [Full Report (PDF)] [Summary (PDF)]
• Metge C, Kozyrskyj A, Roos N (2003). Pharmaceuticals: Focusing on Appropriate Utilization. [Full Report (PDF)] [Summary (PDF)]
• Morgan S, Kozyrskyj A, Metge C, Roos N, Dahl M (2003). Pharmaceuticals: Therapeutic Interchange and Pricing Policies. [Full Report (PDF)] [Summary (PDF)]
• Oxford Centre for Evidence-Based Medicine. http://www.cebm.net/study_designs.asp (ASP). Accessed February 22, 2006.
• Young K. Population Health: Concepts and Methods. 2nd ed. New York: Oxford University Press, 2005.
• Weinberg CR, Umback DM. Choosing a Retrospective Design to Assess Joint Genetic and Environmental Contributions to Risk. Am J Epidemiol 2000; 152(3):197-203. [Abstract]