Risk Estimation

University:
Franklin University
Course:
CAS BI 107 | Biology 1
Academic year:

2020
Views:

258

Pages:

21
Author:

NebulaNomad

PRINCIPLE OF EPIDEMIOLOGY ESTIMATING RISK Absolute Risk 2     The incidence of a disease in a population can indicate the magnitude of the risk in a group of people with a certain exposure It does not indicate whether the exposure is associated with an increased risk of the disease. important implications in both clinical medicine and public health policy. Association of disease and exposure 3   excess risk of the disease Using different type of studies  Observational  Cross sectional, case control, Cohort  Interventional 4 Excess risk 5 Relative Risk (RR) 6 INTERPRETING THE RELATIVE RISK 7     Generally calculated in the cohort studies If RR= 1, the risk in exposed equals the risk in unexposed: no evidence for any association of the disease with the exposure If RR> 1, the risk in exposed is greater than the risk in unexposed: evidence of a positive association, which may be causal If RR< 1, the risk in exposed is less than the risk in unexposed: evidence of a negative association (protective effect) RR 8 9 Odds Ratio (Relative Odds) OR 10  in a case-control study, we do not know the incidence in the exposed or unexposed:  we   cannot calculate the relative risk directly odds ratio (OR), can be obtained from either a cohort or a case-control study and can be used instead of the relative risk. we cannot calculate a relative risk from a casecontrol study, under many conditions we can obtain a very good estimate of the relative risk from a case-control study using the odds ratio. Odds 11  the odds of an event can be defined as the ratio of the number of ways the event can occur to the number of ways the event cannot occur. 12 13 INTERPRETING THE OR 14    If OR= 1, the risk in exposed equals the risk in unexposed: no evidence for any association of the disease with the exposure If OR> 1, the risk in exposed is greater than the risk in unexposed: evidence of a positive association, which may be causal If OR< 1, the risk in exposed is less than the risk in unexposed: evidence of a negative association (protective effect) When OR is a good estimate of RR? 15 1. 2. 3. When the cases studied are representative, with regard to history of exposure, of all people with the disease in the population from which the cases were drawn. When the controls studied are representative, with regard to history of exposure, of all people without the disease in the population from which the cases were drawn. When the disease being studied does not occur frequently. 16 Remember: 17    OR is a useful measure of association in both casecontrol and cohort studies. In a cohort study RR can be calculated directly. In a case-control study RR cannot be calculated directly, so that OR is used as an estimate of the relative risk when the risk of the disease is low. Attributable Risk 18     How much of the disease that occurs can be attributed to a certain exposure? The amount or proportion of disease incidence (or disease risk) that can be attributed to a specific exposure. Attributable risk is in many ways more important in clinical practice and in public health How much of the risk (incidence) of disease can we hope to prevent if we are able to eliminate exposure to the agent in question? AR 19 AR 20  the incidence of a disease that is attributable to the exposure in the exposed group  the proportion of the total incidence in the exposed group that is attributable to the exposure POPULATION ATTRIBUTABLE RISK 21   What proportion of disease in the total population can be attributed to the exposure? If exposure were eliminated, what proportion of the incidence in the total population (which consists of both exposed and unexposed) would be prevented?