![]() Choose the default 95% confidence interval. To analyse these data in StatsDirect select Risk (Retrospective) from the Clinical Epidemiology section of the Analysis menu. The following data represent a retrospective investigation of smoking in relation to oral cancer. The exact calculations can take an appreciable amount of time with large numbers.Īpproximate power is calculated as the power achieved with the given sample size to detect the observed effect with a two-sided probability of type I error of (100-CI%)% based on analysis with Fisher's exact test or a continuity corrected chi-square test of independence in a fourfold contingency table ( Dupont, 1990). Population attributable risk is presented as a percentage with a confidence interval when the odds ratio is greater than or equal to one ( Sahai and Kurshid, 1996).Ī confidence interval (CI) for the odds ratio is calculated using an exact conditional likelihood method ( Martin and Austin, 1991). In order to calculate population attributable risk, the incidence of exposure in the study population must be known or estimated, StatsDirect prompts you to enter this value or to default to an estimate made from your study data. Population attributable risk estimates the proportion of disease in the study population that is attributable to the exposure. In retrospective studies, attributable risk can not be calculated directly but population attributable risk can be estimated. In prospective studies, Attributable risk or risk difference is used to quantify risk in the exposed group that is attributable to the exposure. ![]() Odds ratio is the key statistic for most case-control studies. In epidemiological terms, the odds ratio is used as a point estimate of the relative risk in retrospective studies. The odds ratio ((a/c)/(b/d)) looks at the likelihood of an outcome in relation to a characteristic factor. In retrospective studies you select subjects by outcome and look back to see if they have a characteristic factor such as a risk factor or a protection factor for a disease. risk factor) in the other:Įstimate of population exposure (Px) = c/(c+d)Įstimate of population attributable risk% = 100*(Px*(OR-1))/(1+(Px*(OR-1))) disease status) in one dimension and the presence or absence of a characteristic factor (e.g. You should organize these data into a fourfold table divided by outcome (e.g. The type of data used by this function is counts or frequencies (number of individuals with a study characteristic). If you need information on prospective studies see risk (prospective). The study design considered here is retrospective and usually a case-control study. You can examine the likelihood of an outcome such as disease in relation to an exposure such as a suspected risk or protection factor. This function calculates odds ratios and population attributable risk with confidence intervals. Blackwell Science, Oxford, UK, for more information on methods.Menu location: Analysis_Clinical Epidemiology_Risk (Retrospective). Yates corrected Chi-square statistic and p-value.Uncorrected Chi-square statistic and p-value.Statistical tests for independence calculated include: Relative risk, attributable risk, attributable fraction, population attributable riskĪnd population attributable fraction for cohort or cross-sectional studies.Odds of exposure in cases and controls for case-control studies.Proportion exposed in cases and controls for case-control studies.Incidence/prevalence in exposed/non-exposed cohorts for cohort or cross-sectional studies.Overall proportion of cases for case-control studies.Overall incidence/prevalence for cohort or cross-sectional studies.Measures of association calculated include: Inputs are table values, confidence level required and type of study. Output values (including confidence limits) are calculated for cohort, cross-sectional or case-control studies, as specified. This utility provides summary measures of association and independence for a 2x2 table.
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