Illustrate how improperly selected cases/controls can generate biases in the study. Explore types of Bias generated during clinical studies.

University of Michigan - Ann Arbor

Sutton-Tyrrell, K. (1991). Assessing bias in case-control studies. *AHA Journals*. 22(7),  938-939 from [www.ahajournals.org/doi/pdf/10.1161/01.STR.22.7.938 .](https://www.ahajournals.org/doi/pdf/10.1161/01.STR.22.7.938 .) 

Assessing bias in case-control studies.

Determining the relationship between risk factors and diseases (trait).

Motivation of the study

The paper focusses on case control studies done in a clinical setting. Thus it expands on types of biases generated in this environment. 
The types elucidated are : 
1. Referral Bias
2. Ascertainment Bias
3. Berkson Bias
4. Hospital Control Bias

Types of Bias outlined in paper

The odds ratio is used to measure the association between a factor and a trait in a case controlled study. 
1. An odds ratio >1 implies that the presence of the factor increases the probability of the existence of the trait.
2. An odds ratio <1 implies the opposite i.e. presence of factor inhibits presence  of trait. 
3. An odds ratio =1 implies no impact of the factor on the trait. 

Odds Ratio

Several key conclusions emerge regarding the assessment of bias in case-control studies. First, bias can mask true associations and form false ones, potentially invalidating research findings. Second, there is no universal method to identify all biases; rather, the process is intrinsic to the specific research problem and must be addressed during the study's design phase. Finally, case-control studies are especially susceptible to biases because errors can occur in the selection of either the cases or the controls, both of which can adversely impact or entirely invalidate a study.

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