There are several measures used to quantify the public health impact of exposures and diseases. Relative measures include relative risk (RR) and odds ratio (OR), which indicate strength of association but not absolute impact. Absolute measures include risk difference (RD), attributable risk (AR), and attributable risk percent (AR%), which represent the actual burden of disease preventable by reducing exposure. Population measures include population attributable risk (PAR) and population attributable risk percent (PAR%), which estimate the impact of exposure on the entire population. These measures can be calculated from cohort and population-based case-control studies but usually not regular case-control studies.

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4. Measures of Public Health Impact • Attributable Risk (AR) Number • Attributable Risk Percent (AR%) Percentage • Population Attributable Risk (PAR) Number • Population Attributable Risk Percent (PAR%) Percentage

5. Measures of Public Health Impact IMPORTANT! They all assume (require) that a cause-effect relationship exists between the exposure and the outcome.

6. Relative Risk vs. Attributable Risk Relative Risk: Measure of the strength of association , and indicator used to assess the possibility of a causal relationship. Attributable Risk: Measure of the potential for prevention of disease if the exposure could be eliminated (assuming a causal relationship).

7. Relative Risk vs. Attributable Risk Relative Risk: • Etiology Attributable Risk: • Policy decisions • Funding decisions (e.g. prevention programs)

10. Attributable Risk (AR) Among the EXPOSED: How much of the disease that occurs can be attributed to a certain exposure? AR AR% This is of primary interest to the practicing clinician.

11. Attributable Risk (AR) AR = I exposed – I nonexposed = “Risk Difference” Develop CHD I SM = 84 / 3000 = 0.028 = 28.0 / 1000 I NS = 87 / 5000 = 0.0174 = 17.4 / 1000 (background risk) AR = (28.0 – 17.4) / 1000 = 10.6 / 1000 Smoke Yes No Yes 84 2916 3000 No 87 4913 5000

12. Attributable Risk (AR) AR = (28.0 – 17.4) / 1000 = 10.6 / 1000 Among SMOKERS , 10.6 of the 28/1000 incident cases of CHD are attributed to the fact that these people smoke … Among SMOKERS , 10.6 of the 28/1000 incident cases of CHD that occur could be prevented if smoking were eliminated.

16. Attributable Risk I exposed - I unexposed

17. Figure 12-1 A, Total risks in exposed and nonexposed groups. B, Background risk. C, Incidence attributable to exposure and incidence not attributable to exposure . Downloaded from: StudentConsult (on 8 October 2009 11:44 AM) © 2005 Elsevier

18. Figure 12-2 The concept of attributable risk. Downloaded from: StudentConsult (on 8 October 2009 11:44 AM) © 2005 Elsevier

20. AR: Drunk driving Dead Not dead Risk RD Drunk 45 255 300 0.150 Not d. 135 9565 10000 0.014 0.136

22. Attributable Risk Percent (AR%) AR% = (I exposed – I nonexposed ) / I exposed = “Etiologic fraction” Develop CHD AR% = (28.0 – 17.4) / 28.0 = 37.9% I SM = 84 / 3000 = 0.028 = 28.0 / 1000 I NS = 87 / 5000 = 0.0174 = 17.4 / 1000 (background risk) Smoke Yes No Yes 84 2916 3000 No 87 4913 5000

23. Attributable Risk Percent (AR%) AR% = (28.0 – 17.4) / 28.0 = 37.9% Among SMOKERS , 38% of the morbidity from CHD may be attributed to smoking… Among SMOKERS , 38% of the morbidity from CHD could be prevented if smoking were eliminated.

24. Attributable Risk Percent I exposed – I unexposed RR - 1 ------------------------------- = ------------ x 100% I exposed RR

25. AR%: Fast driving Dead Not dead Risk AR% Fast 100 1900 2000 0.05 Slow 80 7920 8000 0.01 0.05 – 0.01 0.05 = 80%

26. AR%: Drunk driving Dead Not dead Risk AR% Drunk 45 255 300 0.150 Not d. 135 9565 9700 0.014 0.150 – 0.014 150 = 91%

28. Population Attributable Risk (PAR) Among the EXPOSED and NONEXPOSED (e.g. total population): How much of the disease that occurs can be attributed to a certain exposure? PAR PAR% This of interest to policy makers and those responsible for funding prevention programs.

29. PAR and PAR% Example: We want to estimate how much of the burden of diabetes among Tampanians is attributed to obesity.

30. PAR and PAR% CAUTION! In order to calculate PAR and PAR%, we have to be reasonably sure that the results of the study can be generalized to the population of Tampa. (e.g the incidence rates drawn from the sample approximate the incidence rates in the entire population).

31. Population Attributable Risk

32. Population Attributable Risk (PAR) PAR = I total – I nonexposed Diabetes I T = 1100 / 10000 = 0.11 = 110 / 1000 I NE = 250 / 5500 = 0.0455 = 45.5 / 1000 (background risk) PAR = (110 – 45.5) / 1000 = 64.5 / 1000 Weight Yes No Obese 850 3650 4500 Slim 250 5250 5500 1100 8900 10000

33. Population Attributable Risk (PAR) PAR = (110 – 45.5) / 1000 = 64.5 / 1000 In Tampa , 64.5 of the 110/1000 incident cases of diabetes are attributed to obesity … In Tampa , 64.5 of the 110/1000 incident cases of diabetes that occur could be prevented with sufficient weight loss.

35. Population Attributable Risk Percent PAR% = (I total – I nonexposed ) / I total Diabetes PAR% = (110 – 45.5) / 110 = 58.6% I T = 1100 / 10000 = 0.11 = 110 / 1000 I NE = 250 / 5500 = 0.0455 = 45.5 / 1000 (background risk) Weight Yes No Obese 850 3650 4500 Slim 250 5250 5500 1100 8900 10000

36. Population Attributable Risk Percent PAR% = (110 – 45.5) / 110 = 58.6% In Tampa , 59% of the cases of diabetes may be attributed to obesity in the population… In Tampa , 59% of the cases of diabetes could be prevented if Tampa residents lost sufficient weight.

37. PAR: Fast driving Dead Not dead Risk Fast 100 1900 2000 0.05 Slow 80 7920 8000 0.010 180 9820 10000 0.018 PAR = 0.018 – 0.010 = 0.008 PAR% = (0.018 – 0.014) ; 0.018 x 100% = 44%

38. PAR: Drunk driving Dead Not dead Risk Drunk 45 255 300 0.15 Not drunk 135 9565 9700 0.014 PAR = 0.018 – 0.014 = 0.004 PAR% = (0.018 - 0.014) : 0.018 x 100% = 22% 180 9820 10,000 0.018

40. Summary

41. Calculating Measures of Public Health Impact (Case-Control Studies)

44. AR% (Case-Control Studies) (OR – 1) AR% = ----------- x 100 OR

45. Example: AR% (Case-Control Studies) Case-control study to evaluate the impact of smoking as related to bladder cancer. Bladder Cancer (160 / 90) OR = ------------ (120 / 200) = 2.96 Smoke Yes No Yes 160 120 No 90 200

46. Example: AR% (Case-Control Studies) Question: Among smokers , what proportion (percent) of bladder cancer cases can be attributed to their smoking habit? (OR – 1) AR% = ----------- x 100 OR AR% = ((2.96 – 1) / 2.96) x 100 = 66.2%

48. PAR% (Case-Control Studies) (P E ) (OR – 1) PAR% = -------------------- x 100 [(P E ) (OR-1)] + 1 where P E = proportion of exposed controls (assuming that the proportion of exposed controls is representative of the proportion exposed in the source population)

49. Example: PAR% (Case-Control Studies) Case-control study to evaluate the impact of smoking as related to bladder cancer. Bladder Cancer (160 / 90) OR = ------------ (120 / 200) = 2.96 P E = 120 / 320 = 0.375 Smoke Yes No Yes 160 120 No 90 200

50. Example: PAR% (Case-Control Studies) Question: In this study population , what proportion (percent) of bladder cancer cases can be attributed to smoking? (P E ) (OR – 1) PAR% = ---------------------- x 100 [(P E ) (OR-1)] + 1 PAR% = (0.375) (2.96-1) [(0.375) (2.96-1)] + 1 x 100 = 42.4%

54. PF: Vaccine efficacy

55. Annual Death Rates for Lung Cancer and Coronary Heart Disease by Smoking Status, Males 1000 – 500 = 500 per 100,000 127.2 – 12.8 = 114.4 per 100,000 AR 1000 / 500 = 2 127.2 / 12.8 = 9.9 RR 500 12.8 Non-smoker 1,000 127.2 Smoker Coronary Heart Disease Lung Cancer Exposure Annual Death Rate / 100,000

57. Comparison of RR and RD Gerstman Chapter 8 (partial) Smoking causes more heart disease Smoking has a stronger association with lung cancer An exposure can have a strong relative effect (RR) but make a small difference in absolute terms (RD) Lung Cancer and CHD mortality in smokers and non-smokers (per 100,000 person-years) Smokers Non smokers RR RD LungCA 104 10 10.40 94 CHD 565 413 1.37 152

58. Relative Risk vs. Attributable Risk Relative Risk: Measure of the strength of association , and indicator used to assess the possibility of a causal relationship. Attributable Risk: Measure of the potential for prevention of disease if the exposure could be eliminated (assuming a causal relationship).

59. Relative Risk vs. Attributable Risk Relative Risk: • Etiology Attributable Risk: • Policy decisions • Funding decisions (e.g. prevention programs)

60. Summary – Measures of Public Health Impact Measure Cohort study Population-based case-control study Other type of case-control study AR Yes Yes No AR% Yes Yes Yes PAR Yes Yes No PAR% Yes Yes Yes

61. Ringkasan ukuran Tipe Kuantitas Matematis Tanpa denominator Dengan denominator Enumerasi Hitung, angka mutlak Rasio Proporsi Rate

63. Ringkasan ukuran Ukuran dalam epidemiologi Ukuran Frekuensi Penyakit Ukuran asosiasi Ukuran efek /dampak

64. Ukuran frekuensi penyakit Ukuran frekuensi Penyakit Insidens Prevalens Insidens Kumulatif Incidence Density Prevalens titik Prevalens periode Mortalitas

65. Ukuran frekuensi penyakit Ukuran Rasio Risk Ratio Odds Rasio Insidence Density Ratio Prevalence Ratio

66. Ukuran frekuensi penyakit RD = Risk Difference AR = Attributable Risk ER = Excess Risk PAR = Population Attributable Risk PF = Prevented Fraction Ukuran Efek /dampak Perbedaan efek Fraksi Efek RD AR ER PAR AR% PAR% PF

68. Epidemiology Kept Simple Chapter 8 Measures of Association Gerstman Chapter 8 (partial)