Study Design 101
If the outcome of interest is uncommon, however, the size of prospective investigation required to estimate relative risk is often too large to be feasible. In retrospective studies the odds ratio provides an estimate of relative risk. You should take special care to avoid sources of bias and confounding in retrospective studies.
Prospective investigation is required to make precise estimates of either the incidence of an outcome or the relative risk of an outcome based on exposure. Case-Control studies are usually but not exclusively retrospective, the opposite is true for cohort studies. The following notes relate case-control to cohort studies:.
Results of case-control studies have been frequently used in safety evaluations at FDA, primarily to add further information to the overall assessment of safety. In the past, FDA has supported case-control studies on compounds of interest, such as the National Bladder Cancer Study and the use of artificial sweeteners. In addition, FDA often looks carefully at the results of case-control studies in the setting of outbreaks of food-borne disease to identify the food vehicle that was most likely responsible for transmitting the infectious agent.
The results then can be used to help target specific food vehicles for microbiologic testing as a means of recovering the pathogen from the implicated food. Meta-analysis has been defined as "the statistical analysis of a large collection of analysis results from individual studies for the purpose of integrating the findings".
Several publications in the peer-reviewed literature serve as guidelines for the appropriate conduct of meta-analysis, 6 , 7 the principal components of which include:.
Field Epidemiology Manual
Where FDA evaluates a meta-analysis, the Agency considers such an analysis primarily as supporting evidence, rather than as primary evidence, that can confirm the validity of data concerning a hypothesis. The Agency must carefully scrutinize each meta-analysis to assess the soundness of its design and the quality of the data from individual studies to determine the significance of the data.
Such scrutiny requires review of the original studies used for the meta-analysis. Anonymous Reviews and Commentary. Guidelines for documentation of epidemiologic studies.
- Case-control study in medical research: Uses and limitations?
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- Chapter 9. Case–Control Studies | Medical Epidemiology, 4e | AccessMedicine | McGraw-Hill Medical.
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Bailar, J. New Eng. Glass, G. Henkel, J. FDA's 'heads up' on medical product safety.
Principles of Epidemiology | Lesson 1 - Section 7
Last, J. Abramson, S. Greenland, M. Tuhriaus, associate eds. Amsel, assistant ed. Sacks, H. New Engl. Issued by: Guidance Issuing Office. It does not create or confer any rights for or on any person and does not operate to bind FDA or the public. They then need to be taken into account in the interpretation of the results of the study. If possible, the direction of the bias overestimation or underestimation and the magnitude of the bias also should be discussed.
While case-control and cohort studies are both susceptible to bias , the case-control study is affected by more sources of bias. Through our study design, we can try to minimise selection bias and prevent information bias in cohort and case-control studies. In epidemiological studies, all efforts should be made to avoid biasing the selection of study participants. Information on characteristics of the non-responders should be obtained if possible e. This can give important insights into the extent of selection bias.
Information measurement biases can be easier to prevent and measure than selection biases . Approaches taken to prevent recall bias include:.
Rothman KJ. Epidemiology - An Introduction. New York: Oxford University Press; Introduction to Epidemiology.
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Black N, Raine R, editors. Sackett DL.
Bias in analytic research. J Chronic Dis. Quantifying the impact of selection bias caused by nonparticipation in a case-control study of mobile phone use. Ann Epidemiol. McCarthy N, Giesecke J. Case-case comparisons to study causation of common infectious diseases. Int J Epidemiol.
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