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Epidemiological Study Design

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Jari Haukka

on 11 September 2013

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Transcript of Epidemiological Study Design

Goal: To Obtain Valid and Precise Information on Association Between Exposure and Disease Using a Minimum of Resources
Research question involves a
prevention, treatment, or
causal factor.

Moderate or large effect expected.
Trial not ethical or feasible.
Trial too expensive.
Research question involves a prevention or treatment.
Small effect expected.
Ethical and feasible.
Money is available.
Little known about disease.
Evaluate many exposures.
Disease is rare.
Disease has long induction and latent period.
Exposure data are expensive.
Underlying population is dynamic.
Little known about exposure.
Evaluate many effects of an
Exposure is rare
Underlying population is fixed.
Disease has short induction and latent period.
Current exposure.
Want high-quality data.
Disease has long induction and latent period.
Historical exposure.
Want to save time and money.
Select study design
Examine rates of disease in relation to a population-level factor.
Population-level factors include summaries of individual population members, environmental measures, and global measures.
Study groups are usually identified by place, time, or a combination of the two.
Limitations include the ecological fallacy and lack of information on important
Advantages include low cost, wide range of exposure levels, and the abilityto examine contextual effects on health.
Examine association at a single point in time, and so measure exposure prevalence in relation to disease prevalence.
Cannot infer temporal sequence between exposure and disease if exposure is a changeable characteristic.
Other limitations may include preponderance of prevalent cases of long duration and healthy worker survivor effect.
Advantages include generalizability and low cost.
Ecologic studies
A classical ecologic study examines the rates of disease in relation to a factor described on a population level. Thus, “the units of analysis are populations or groups of people rather than individuals.”

The lack of individual-level information leads to a limitation of ecologic studies known as the “ecological fallacy” or “ecological bias.” The ecological fallacy means that “an association observed between variables on an aggregate level does not necessarily represent the association that exists at the individual level.”

In other words, one cannot necessarily infer the same relationship from the group level to the individual level.
Ecological fallacy
We study the following paper:

Ahern, Thomas P., Lars Pedersen, Maja Tarp, Deirdre P. Cronin-Fenton, Jens Peter Garne, Rebecca A. Silliman, Henrik Toft Sørensen, and Timothy L. Lash. 2011. “Statin Prescriptions and Breast Cancer Recurrence Risk: A Danish Nationwide Prospective Cohort Study.” Journal of the National Cancer Institute. doi:10.1093/jnci/djr291. http://jnci.oxfordjournals.org/content/early/2011/08/01/jnci.djr291.abstract.

Please answer the following questions:
How was the study population defined
How was the statin exposure defined (yes/no, amount)
Was there any dose-response checked
Which limitations of ther study your think are the most important
Case Study: Cohort Study
We study the following paper:

Please answer the following questions:
How was the study population defined?
Did choice of model have any effect on results?
If there differences, how would you interpret them?
Which research question is, in you opinion,: most relevant (p 267, left column):

1) Estimate the average treatment effect in a population whose distribution of risk factors is equal to that for the t-PA-treated patients only .

2) Estimates the average effect of treatment in the entire study population, that is, for patients who were and were not treated with t-PA.
Case Study: Cohort Study
Case Study:
Case-control study
Kurth, Tobias, Alexander M. Walker, Robert J. Glynn, K. Arnold Chan, J. Michael Gaziano, Klaus Berger, and James M. Robins. 2006. “Results of Multivariable Logistic Regression, Propensity Matching, Propensity Adjustment, and Propensity-based Weighting under Conditions of Nonuniform Effect.” American Journal of Epidemiology 163 (3) (February 1): 262 -270. doi:10.1093/aje/kwj047.
Epidemiological Study Design
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