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Understanding Cohort Study Analysis: Measures of Exposure and Outcome Relationships

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fitzgerald-benjamin
20 diapositives · 349 Views · Nov 14, 2014

This guide delves into cohort study analysis, focusing on the relationship between exposure and outcome using various metrics. Key measures include cumulative incidence, incidence rate, relative risk (RR), attributable risk (AR), and odds ratio (OR). The document explains how to calculate these metrics, differences between relative and attributable risk, and their implications in public health. Explore how these measures quantify risks within exposed and unexposed populations, providing crucial insights for epidemiological research and health policy.

#understanding cohort study analysis: measures of exposure and outcome relationships #understanding cohort study analysis: measures of exposure and outcome relationships ppt #powerpoint #presentation
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  1. Cohort Study Analysis

  2. Standard 2 X 2 table(Relation between exposure and outcome)

  3. Two types of measures for rate • Cumulative incidence = Proportion of study subjects getting the outcome during the study period • Incidence rate = New cases/ Person-time under observation

  4. Comparing risks in different groups • Relative risk OR Risk ratio (RR) • Attributable risk OR Risk difference (AR) • Attributable risk percent (AR%) • Population attributable risk (PAR) • Population attributable risk percent (PAR%) • Odds Ratio (OR)

  5. Relative risk OR Risk ratio • Ratio of the risk among exposed to the risk among unexposed [Risk (Exp) / Risk (Unexp)] • Risk of disease among exposed = [a/ [a+ b)] • Risk of disease among unexposed = [c/ [c +d)] • RR = [a/ [a +b)] / [c/ [c +d)] • For null hypothesis, Risk ratio will equal ‘one’

  6. Risk difference vs. Relative risk 22 Relative risk Absolute risk 1

  7. Attributable risk OR Risk difference (Absolute differences in risks or rates) • Attributable Risk = Risk (Exp) – Risk (Unexp) • Risk of disease among exposed = [a/ [a +b)] • Risk of disease among unexposed = [c/ [c +d)] • Risk difference = [a/ [a +b)] - [c/ [c +d)] • For null hypothesis, Risk difference will equal ‘zero’

  8. Risk difference vs. Relative risk Risk difference Absolute risks(Exp & Unexp)

  9. Attributable risk percent among exposed • Among exposed, what percent of the total risk for disease is due to the exposure • AR% (Exposed) = [Risk (Exp) – Risk (Unexp)]/ Risk (Exp) X 100 = (RR – 1)/ RR X 100 = (OR – 1)/ ORX 100(if risk is small)

  10. Attributable Risk Percent 22 % risk due to exposure Absolute risks (Exp) Relative risk % risk due to background 1

  11. Attributable Risk Percent p0RR p0RR Relative risk p0(RR-1) p0 1 Attributable risk Percent = (RR-1)/ RR *100

  12. Population attributable risk • In the general population, how much of the total risk for disease is due to the risk factor • Risk (Exp) – Risk (Unexp) • Risk (Total) = [Proportion population Exp X Risk (Exp)] + [Proportion population Unexp X Risk (Unexp)]

  13. Population attributable risk percent • Among the general population, what percent of the total risk for disease is due to the risk factor • PAR% = [Risk (Exp) – Risk (Unexp)]/ Risk (Total) X 100 = [Pe (RR – 1)]/ [1+ Pe (RR – 1)] X 100

  14. 180 160 140 120 Absolute risk of lung cancer death per 100,000 adult male per year 100 80 60 40 20 0 Smoker Nonsmoker Population attributable risk percent RR Pe(RR-1) (RR-1)(1-Pe) Pe (1-Pe) 1 Population Attributable risk Percent = [Pe (RR – 1)]/ [1+ Pe (RR – 1)] X 100

  15. Odds Ratio • Ratio of the odd among exposed to the odd among unexposed [Odd (Exp) / Odd (Unexp)] • Odd of disease among exposed = [a/ b] • Odd of disease among unexposed = [c/ d] • OR = [a/ b] / [c/ d] = ad/ bc • RR = [a/ a+b] / [c/ c+d] • For null hypothesis, Risk ratio will equal ‘one’ • Under most circumstances, the OR is a good estimate of RR; thus may be used as an estimate of RR

  16. Odds ratio in a Cohort study • An important measure in cohort study also • Link between case control study and cohort study • Link to mainstream analytical process – Logistic regression • What if we are interested in reverse of the event (survival and not death; non-disease and not diseased)

  17. Which side is up in the risk ratio or odds ratio?

  18. Absolute and Relative risk reduction

  19. Risk Reduction • Risk (T/t) = a/(a+b) • Risk (Exp) = c/(c+d) • RR = Risk (T/t)/ Risk (Exp) • ARR = Risk (Exp) – Risk (T/t) • RRR = [Risk (Exp) – Risk (T/t)] / Risk (Exp) = 1-Risk(T/t)/Risk(Exp) = 1-RR • NNT = 1/ARR = 1/Risk(Exp)*RRR • NNH

  20. Thank you