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Ratios and Rates

Ratios and Rates

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Ratios and Rates

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  1. Ratios and Rates Bioterrorism Epidemiology Module 7 Missouri Department of Health And Senior Services

  2. Learning Objectives • To understand how epidemiologists use ratios and rates • To understand the difference between ratios and rates • To identify the different types of ratios and rates • To calculate different ratios and rates

  3. Ratio • The relationship between two numbers in the form x:y or x/y,used when the population at risk is unknown

  4. Number of Deaths by Census Tract Deaths Census Tract Number

  5. Mortality Ratio Deaths Census Tract Number

  6. Mortality Ratio Deaths Census Tract Number

  7. Mortality Ratio Deaths Census Tract Number

  8. Mortality Ratio 90 to 20 or 4.5 to 1 Deaths Census Tract Number

  9. Proportion • Specific type of ratio in which the numerator is included in the denominator. The resultant value can be expressed as a percentage by multiplying by 100

  10. Mortality Ratio Deaths Census Tract Number

  11. Mortality Ratio Deaths Census Tract Number

  12. Proportion of Deaths in Census Tract 103 90 155 =.58

  13. Proportion of Deaths in Census Tract 103 90 X 100 155 =.58

  14. Rate • Most important tool for measuring disease in epidemiology • Rate is a special form of proportion that includes specification of time • Basic measure of disease occurrence • Measure that most clearly expresses probability or risk of disease

  15. Rate Defined Number of events in a specific time period Population at risk of these events in a specific time period * k k = some measure of reporting such as per 100, per 1,000, per 100,000

  16. Crude Death Rate CDR = Number of deaths among people in an area during a specific time period Number of people in the area during that time period

  17. Crude Death Rate CDR = Number of deaths among people in an area during a specific time period Number of people in the area during that time period *1000

  18. Crude Death Rate Number of deaths among people in an area during a specific time period Number of people in the area during that time period *1000 2500 people attended soccer match

  19. Crude Death Rate Number of deaths among residents in an area during a specific time period Average population in the area during that time period *1000 2500 people attended soccer match 775 people died

  20. Crude Death Rate Number of deaths among people in an area during a specific time period Number of people in the area during that time period *1000 775/2500 = .31 * 1000 = 310 per 1000

  21. Age-specific Mortality Rate ASMR = Number of deaths among residents in a specified age range in an area during a specified time period Number of people in that age range in the area during that time period

  22. Age-specific Mortality Rate Number of deaths among residents aged 25-45 in an area during a specified time period Number of people in the age range 25-45 in the area during that time period

  23. Age-specific Mortality Rate Number of deaths among residents aged 25-45 in an area during a specified time period Number of people in the age range 25-45 in the area during that time period 6/9 = .67 * 1000 = 670 per 1000

  24. Standardized Mortality Ratio Observed deaths Expected deaths SMR =

  25. Standardized Mortality Ratio If you are provided with an expected death rate of 200 per 1000 people, what is the SMR using the data from the following table? Observed deaths Expected deaths SMR =

  26. Standardized Mortality Ratio If you are provided with an expected death rate of 200 per 1000 people what is the SM? 13/25 or 520/1000 200/1000 SMR = = 2.6 or 260

  27. Cause-Specific Mortality Rate CSMR = Number of deaths from a specific cause among residents in an area during a specified time period Number of people in the area during that time period

  28. Cause-Specific Mortality Rate What is the CSMR for Respiratory Disease in Table 1 in the appendix? Number of deaths from a specific cause among residents in an area during a specified time period Average population in the area during that time period

  29. Cause-Specific Mortality Rate What is the CSMR for Respiratory Disease in Table 1? 22/156 = .15 or .15 * 1000 = 150 per 1000 Number of deaths from respiratory disease among residents in an area during a specified time period Number of people in the area during that time period

  30. Cause-Specific Mortality Rate What is the CSMR for Cardiovascular Disease in Table 1 of your workbook for the study group and for the control group? Number of deaths from a specific cause among residents in an area during a specified time period Average population in the area during that time period

  31. Cause-Specific Mortality Rate What is the CSMR for cardiovascular disease for the control group in Table 1? 21/55 = .38 or .38 * 1000 = 380 per 1000 Number of deaths from respiratory disease among residents in an area during a specified time period Number of people in the area during that time period

  32. Cause-Specific Mortality Rate What is the CSMR for cardiovascular Disease for the study group in Table 1? 34/101 = .34 or .34 * 1000 = 340 per 1000 Number of deaths from respiratory disease among residents in an area during a specified time period Number of people in the area during that time period

  33. Proportionate Mortality Ratio PMR = Number of deaths from a given cause in a specific time period Total deaths in the same time period

  34. Proportionate Mortality Ratio What is the PMR for Cardiovascular disease in Table 1 in the appendix? Number of deaths from a given cause in a specific time period Total deaths in the same time period

  35. Proportionate Mortality Ratio What is the PMR for Cardiovascular disease in Table 1? 55/75 = .73 = 73% Number of deaths from a given cause in a specific time period Total deaths in the same time period

  36. Attack Rate (Cumulative Incidence Rate) Number of people at risk who develop a certain illness over specified time period Total number of people at risk of developing that illness at beginning of time period

  37. Attack Rate (Cumulative Incidence Rate) What is the attack rate for Gastroenteritis from Table 2 in the appendix? Number of people at risk who develop a certain illness over specified time period Total number of people at risk of developing that illness at beginning of time period

  38. Attack Rate (Cumulative Incidence Rate) What is the attack rate for Gastroenteritis from Table 2? 46/75 = .61 or 61% Number of people at risk who develop a certain illness over specified time period Total number of people at risk of developing that illness at beginning of time period

  39. Food-Specific Attack Rate Number of people who ate a certain food and became ill Total number of people who ate that food

  40. Food-Specific Attack Rate Referring to Table 2, what is the attack rate for jello? Number of people who ate a certain food and became ill Total number of people who ate that food

  41. Food-Specific Attack Rate Referring to Table 2, what is the attack rate for jello? 17/24 = .71 or 71% Number of people who ate a certain food and became ill Total number of people who ate that food

  42. Case Fatality Rate CFR = Number of deaths from a disease Number of clinical cases of that disease Number of deaths from a disease Population at risk of acquiring a disease MR =

  43. Case Fatality Rate What is the case fatality rate for respiratory illness from Table 3? Number of deaths from a disease Number of clinical cases of that disease

  44. Case Fatality Rate What is the case fatality rate for respiratory illness from Table 3? 13/25 = .52 or 52% Number of deaths from a disease Number of clinical cases of that disease