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# Measuring of risk

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### Measuring of risk

1. 1. Measuring of Risk Prepared By: Dr.Anees AlSaadi CMT-P R4 December 2013 1
2. 2. Measuring of Risk Introduction: Exposure Link / Relation Disease 2
3. 3. Measuring of Risk Introduction: • Is there an association between Exposure and Disease …? • Do persons with exposure have higher level of disease than persons without exposure…? • Is the association real (causal) 3
4. 4. Measuring of Risk Introduction: Epidemiology determine the relationship or association between a given exposure and frequency of disease in population. 4
5. 5. Measuring of Risk Introduction: Epidemiology does not determine the cause of a disease in a given individual. 5
6. 6. Measuring of Risk Introduction: 6
7. 7. Measuring of Risk 7
8. 8. Measuring of Risk Measures of association: • The key to epidemiological analysis is comparison. • A measure of association quantifies the relation ship between the exposure and disease among the comparison groups. 8
9. 9. Measuring of Risk Measures of association: Examples of Measure of Association: Risk Ratio (Relative Risk). Odds Ratio. Attributable proportion. 9
10. 10. Measuring of Risk Measures of association: Risk Ratio • Called also relative risk. • Compares the risk of a health event among one group with the risk among another group. 10
11. 11. Measuring of Risk Measures of association: Risk Ratio(RR) Risk Ratio (RR)= Risk of disease in group of primary interest Risk of disease in comparison group 11
12. 12. Measuring of Risk Measures of association: Risk Ratio(RR) RR less than 1.0 Indicates a decrease risk for the exposed group. Indicating that perhaps exposure actually protects against disease occurrence. RR of 1.0 Indicates identical risk among the two groups. RR of more than 1.0 Indicates an increase risk for the group in the numerator usually the exposed group. 12
13. 13. Measuring of Risk Measures of association: Risk Ratio(RR) Ill Well Total Exposed a b a+b Unexposed c d c+d Total a+c b+d a+ b+ c+ d 13
14. 14. Measuring of Risk Measures of association: Risk Ratio(RR) Example In outbreak of T.B among prison inmates in South Carolina in 1999, 28 of 157 inmates residing on the east wing of the dormitory developed T.B, compared with 4 of 137 inmates residing on the west wing. 14
15. 15. Measuring of Risk Measures of association: Risk Ratio(RR) T.B + T.B - Total East Wing a=28 b=129 a + b=157 West Wing c= 4 d=133 c + d=137 Total a+c=32 b+d= 262 a+ b+ c+ d=294 Risk of T.B among East Wing residents= 28/157 X100= 17.8% Risk of T.B among West Wing residents=4/137X100= 2.9% RR= 17.8/2.9= 6.1 The inmates who resided in the East wing of the dormitory were 6.1 times as likely to develop T.B as those who resided in the West wing. 15
16. 16. Measuring of Risk Measures of association: Risk Ratio(RR) Example In an outbreak of varicella in Oregon in 2002, varicella was diagnosed in 18 of 152 vaccinated children compared with 3 of 7 unvaccinated children. Calculate the risk ratio..? 16
17. 17. Measuring of Risk Measures of association: Risk Ratio(RR) Varicella + Varicella - Total Vaccinated 18 134 152 Unvaccinated 3 4 7 Total 21 138 159 Risk of varicella among vaccinated children= 18/152 X100=11.8% Risk of varicella among unvaccinated children= 3/7X100= 42.9% RR=11.8/42.9=0.28 The vaccinated children were only approximately as one fourth to develop varicella 17 as were unvaccinated children.
18. 18. Measuring of Risk Measures of association: Risk Ratio(RR) RR is mostly used in Cohort Studies Can be Used also in Cross sectional as well as Clinical trails. 18
19. 19. Relative risk calculator 19
20. 20. Interpretation Patients/ Subjects / Individuals. Exposure, Risk factor (RR Value) as likely to develop Outcome/ Disease/ Conditions/ event 20
21. 21. Measuring of Risk Measures of association: Odds Ratio(OD) Is another measure of association that quantifies the relation ship between an exposure with two categories and health problem. 21
22. 22. Measuring of Risk Measures of association: Odds Ratio(OD) In statistics, an odds of an event is the ratio of: the probability that the event WILL occur to the probability that the event will NOT occur 22
23. 23. Measuring of Risk Measures of association: Odds Ratio(OD) In simpler term, an odds of an event can be calculated as: Number of events divided by number of non-events 23
24. 24. Measuring of Risk Measures of association: Odds Ratio(OD) 24
25. 25. Measuring of Risk Measures of association: Odds Ratio(OD) 25
26. 26. Measuring of Risk Measures of association: Odds Ratio(OD) Example Disease+ Disease- Total Exposed 100 1900 2000 Not Exposed Total 80 180 7920 9820 8000 10000 OD= 100X7920 / 1900X80 = 5.2 26
27. 27. Interpretation Exposed Subjects/ Individuals .. Case / disease/ Event … Odds Ratio Value Controls without the exposure 27
28. 28. Measuring of Risk Measures of association: Odds Ratio(OD) Example A case control study was conducted in Hamad Hospital to compare 35 lung cancer cases to controls to determine the associated factors related to lung cancer. Out of 117 subjects in the sample, 88 were daily smokers. Only two cases were found to be nonsmokers. Calculate the Odds Ratio and interpret it. ? 28
29. 29. Cases Lung Cancer Controls Without Lung Cancer Total Daily Smokers Nonsmokers 33 55 88 2 27 29 Total 35 82 117 Odds Ratio = 33X 27 / 2X55 = 8.1 Daily Smokers showed risk of having lung cancer 8.1 times that of nonsmokers. 29
30. 30. Measuring of Risk Measures of association: Odds Ratio(OD) 30
31. 31. Odds Ratio calculator 31
32. 32. Any relation between RR and OR ….? 32
33. 33. Any relation between RR and OR ….? Relative Risk Odds Ratio • Needs incidence of the disease. • Incidence not for its calculation. • Usually in Prospective, cross • Retrospective studies and in sectional and clinical trail cross sectional. Studies. • Good estimate for RR in case of • demonstrates temporality. low frequency disease. • OR can overestimate risk, in rare disease. 33
34. 34. Measuring of Risk Measures of association: Attributable proportion • Called also attributable risk percent. • Is a measure of the public health impact of a causative factor. 34
35. 35. Measuring of Risk Measures of association: Attributable proportion The calculation of this measure assumes that occurrence of disease in the unexposed group represent the baseline or expected risk for that disease. 35
36. 36. Measuring of Risk Measures of association: Attributable proportion It assumes that if the risk of disease in the exposed group is higher than the risk in the unexposed group, the difference can be attributed to the exposure. 36
37. 37. Measuring of Risk Measures of association: Attributable proportion The attributable proportion is the amount of the disease in the exposed group attributable to the exposure. 37
38. 38. Measuring of Risk Measures of association: Attributable proportion 38
39. 39. Measuring of Risk Measures of association: Attributable proportion Attributable proportion= Risk for exposed group – risk for unexposed group x 100% Risk for exposed group 39
40. 40. Measuring of Risk Measures of association: Attributable proportion Example A study of smoking and lung cancer, the lung cancer mortality rate among nonsmokers was 0.07 per 1,000 persons per year. The lung cancer mortality rate among who smoked 1-14 cigarettes per day was 0.57 lung cancer deaths per 1,000 persons per year. Calculate the attributable proportion? 40
41. 41. Measuring of Risk Measures of association: Attributable proportion Attributable proportion = (0.57 – 0.07) / 0.57X 100%= 87.7% About 88% of the lung cancer among smokers of 1-14 cigarettes per day might be attributable to their smoking. 41
42. 42. • Relative risk and odds ratio are important as measures of the strength of association – Important for deriving causal inference. • Attributable risk is a measure of how much disease risk is attributed to a certain exposure – Useful in determining how much disease can be prevented. 42
43. 43. Relative risk is valuable in etiologic studies of disease. Attributable risk is useful for Public Health guidelines and planning. 43
44. 44. Practical Exercise 44
45. 45. Practical Exercise 45
46. 46. 46