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Understanding Measures of Risk and Association in Public Health

Learn how to measure and compare risks in public health using concepts like Relative Risk, Attributable Risk, and Odds Ratio. Discover how these measures help in identifying and preventing health issues effectively.

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Understanding Measures of Risk and Association in Public Health

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  1. Measures of risk and association

  2. Risk Likelihood of having a disease or any health phenomenon. - How can you measure the risk? Risk is measured by Rate (incidence, prevalence, mortality,…..) - How do you know that this risk is high or low? By risk comparison

  3. Examples of risk comparison: risk ratio (relative risk), attributable risk, rate ratio, odds ratio.

  4. Relative Risk (Risk Ratio) • It compares the risk of some health-related event such as disease or death in two groups regarding risk factor. • RISK FACTOR: sex, age, race, or exposure to any suspected risk (SE, food, chemical, behavior ….. ). • The group of primary interest is labeled as “exposed” group, and the comparison group is labeled as “unexposed” group. • “exposed” group .. numerator; • “unexposed” group ..denominator: Risk Ratio (RR) = incidence among exposed group incidence among non exposed

  5. Relative Risk (Risk Ratio) • Relative risk ( RR),Risk Ratio • Estimates the magnitude of an association between exposure & disease. • Which is important in the causation & in the policy of prevention.

  6. Start Outcome Family smoker 500 children Exposed Diseased 300 Children (<12 yrs) 1000 Not diseased 200 1 year Diseased 120 Family non-smoker 500 children Not exposed Not diseased 380

  7. Rate: Incidence rate • Incidence of Resp. Infection among exposed children: 300 • 500 * 100 = 60% • Incidence of Resp. Infect. Among non exposed children: 120 • 500 *100 = 24%

  8. Cohort Study(cont.) Relative RiskIncidence rate among exposed Risk Ratio = Incidence rate in non exposed. 60% 24% = 2.5 ? RR = 1: means zero (no effect of the exposure) RR > 1: means (positive effect of the exposure) RR < 1: means negative effect of exposure (protective)

  9. Attributable risk (AR), Risk difference: • Excess risk of the disease in those exposed compared with those none exposed. • AR = Ie – Io

  10. Base-line risk Incidence A R I. among non exposed I. among exposed

  11. Attributable Risk: 60% - 24% = 36% 36% of Resp. Infection among <12 children can be attributed to family smoking.

  12. AR%(Attributable proportion): • pop. risk • The percentage of cases which could be prevented if we remove the exposure to that factor. • AR% = Ie – Io * 100 Ie AR% = 36% / 60% = 60% ?

  13. Rate Ratio A rate ratio compares two groups in terms of , person-time rates, or mortality rates. Rate ratio = rate for group of primary interest rate for comparison group The interpretation of the value of a rate ratio is similar to that of the risk ratio.

  14. Doll and Hill study : Mortality of British doctors cited from Mausner, 1985

  15. Odds ratio • Is another measure of association. • It is a measure of choice for case-control study. • quantifies the relationship between an exposure and health outcome from a comparative study. The odds ratio is calculated as: Odds ratio = ad bc a = No. of persons with disease and with exposure of interest b = No. of persons without disease, but with exposure of interest c = No. of persons with disease, but without exposure of interest d = No. of persons without disease & without exposure of interest a + c = total number of persons with disease (“cases”) b + d = total number of persons without disease (“controls”)

  16. Case Control Studies CROSS -RATIO

  17. The measure of association between the risk factor and the disease in a case-control is calculated by “odds ratio” (OR)“Odds of factor among cases divided by odds of factor among control”OR =

  18. Example: A study of TB with certain exposure in a Hypothetical case-control study. RiskFactor OR= 100x140 / 40x80 = 4.4 TB was 4 times more among those with bad nutrition than those who are not.

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