Odds ratio, Relative risk, Attributable risk, Population attributable risk

Odds ratio (OR) is a measure of association between an exposure and an outcome. OR represents odds that an outcome will occur given a particular exposure, compared to the odds of outcome occurring in absence of that exposure. Odds ratios are most commonly used in case-control studies, however they can also be used in cross-sectional and cohort study designs as well (with some modifications and/or assumptions).

Odds ratios are used to compare relative odds of the occurrence of the outcome of interest (e.g. disease or disorder), given exposure to the variable of interest (e.g. health characteristic, aspect of medical history). The odds ratio can also be used to determine whether a particular exposure is a risk factor for a particular outcome, and to compare the magnitude of various risk factors for that outcome.

1.  OR=1 Exposure does not affect odds of outcome

2.  OR>1 Exposure associated with higher odds of outcome                        

3.  OR<1 Exposure associated with lower odds of outcome                    

Relative risk (RR): A synonym for risk ratio. However, the term is also commonly

used to refer to the rate ratio and even to the odds ratio (OR). To minimize confusion,

it may be better to avoid this term in favor of more specific terms.

Rate ratio The ratio of two rates; e.g., the rate in an exposed population divided by the rate

in an unexposed population.

Relative Risk (RR) = (incidence in exposed)/(incidence in non-exposed)

Attributable risk (AR) = (incidence in exposed - incidence in non-exposed)/(incidence in exposed)

Risk difference (RD) = (incidence in exposed - incidence in non-exposed)

Population attributable risk (PAR) = (incidence total- incidence in non-exposed)/(incidence total)

or PAR =  P_e (RR_e-1)  /  [1 + P_e (RR_e-1)]

where, Pe is prevalence of exposure

RRe is relative risk of that exposure

Ie - incidence in exposed

Iu - incidence in unexposed (non-exposed)

Ip - incidence total (exposed + nonexposed)

PSM / COMMUNITY MEDICINE by Dr Abhishek Jaiswal is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
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