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Basic measurements in epidemiology

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Rate, Ratio, Proportion, Measures of mortality, Measures of morbidity

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Basic measurements in epidemiology

  1. 1. Basic measurements in epidemiology Dr. S. A. Rizwan, M.D., Asst. Professor, Department of Community Medicine, VMCHRI, Madurai
  2. 2. Learning objectives • At the end of this lecture you sh be able • List the various tools used for measurement • List the various measures of death • List the various measures of disease 2
  3. 3. Recap • Define epidemiology • Uses of epidemiology 3
  4. 4. Measurements used in epidemiology • Measurement of mortality • Measurement of morbidity • Measurement of disability • Measurement of natality • Measurement of disease attributes • Measurement of health care services • Measurement of the risk factors • Measurement of demographic variables 4
  5. 5. TOOLS OF MEASUREMENT 5
  6. 6. Tools of measurement • Proportion • Rate • Ratio 6
  7. 7. Proportion • Usually expressed as a percentage % – Numerator (which is part of denominator) – Denominator – Multiplier – No time factor 7
  8. 8. Proportion – example What proportion of this class are Vijay fans? 8
  9. 9. Proportion – example What proportion of this class are Ajith fans? 9
  10. 10. Proportion – ‘real’ example • What proportion of the population is suffering from diabetes? 10
  11. 11. Rate Contains • Numerator (which is part of denominator) • Denominator • Multiplier • Time period • Usually expressed per 100 / per 1000 population • It has a time dimension, whereas a PROPORTION does not 11
  12. 12. Rate – example 12
  13. 13. Rate – example • Death rate = 𝑁𝑜.𝑜𝑓 𝑑𝑒𝑎𝑡ℎ𝑠 𝑖𝑛 𝑜𝑛𝑒 𝑦𝑒𝑎𝑟 𝑇𝑜𝑡𝑎𝑙 𝑝𝑜𝑝𝑢𝑙𝑎𝑡𝑖𝑜𝑛 𝑖𝑛 𝑡ℎ𝑎𝑡 𝑦𝑒𝑎𝑟 X 1000 13
  14. 14. Ratio Contains • Numerator (not part of denominator) • Denominator 14
  15. 15. Ratio – example 15
  16. 16. Ratio – example 16
  17. 17. Ratio – example 17
  18. 18. Summary • Epidemiology uses 3 main tools of measurement – Proportion – Rate – Ratio 18
  19. 19. MEASUREMENT OF MORTALITY 19
  20. 20. Measurement of mortality • Crude death rate • Specific death rate • Proportional mortality rate • Case fatality rate • Survival rate • Adjusted/standardized rates 20
  21. 21. International death certificate 21
  22. 22. Crude Death Rate 𝐶𝐷𝑅 = 𝑁𝑜.𝑜𝑓 𝑑𝑒𝑎𝑡ℎ𝑠 𝑑𝑢𝑟𝑖𝑛𝑔 𝑜𝑛𝑒 𝑦𝑒𝑎𝑟 𝑀𝑖𝑑 𝑦𝑒𝑎𝑟 𝑝𝑜𝑝𝑢𝑙𝑎𝑡𝑖𝑜𝑛 X 1000 22
  23. 23. Total population in Madurai in 2015 23
  24. 24. No. of deaths in Madurai in 2015 24
  25. 25. CDR in Madurai in 2015 25
  26. 26. Specific death rate • Cause specific – Deaths due to cholera • Age specific – Infant deaths • Sex specific – Maternal deaths • Time specific – Weekly deaths 26
  27. 27. Total population in Madurai in 2015 27
  28. 28. No. of deaths in Madurai in 2015 28
  29. 29. Cause of death – cholera 29
  30. 30. Cholera specific death rate in Madurai in 2015 30
  31. 31. Proportional mortality rate = 𝑁𝑜.𝑜𝑓 𝑑𝑒𝑎𝑡ℎ𝑠 𝑑𝑢𝑒 𝑡𝑜 𝑎 𝑝𝑎𝑟𝑡𝑖𝑐𝑢𝑙𝑎𝑟 𝑐𝑜𝑛𝑑𝑖𝑡𝑖𝑜𝑛 𝑇𝑜𝑡𝑎𝑙 𝑛𝑜.𝑜𝑓 𝑑𝑒𝑎𝑡ℎ𝑠 X 100 31
  32. 32. Total population in Madurai in 2015 32
  33. 33. No. of deaths in Madurai in 2015 33
  34. 34. Total deaths 34
  35. 35. Cause of death – cholera 35
  36. 36. Proportional mortality rate of cholera 36
  37. 37. 37 Total population (MYP) Total deaths – all causes Cholera deaths CDR Specific DR PMR
  38. 38. Case fatality rate CFR = 𝑁𝑜.𝑜𝑓 𝑑𝑒𝑎𝑡ℎ𝑠 𝑑𝑢𝑒 𝑡𝑜 𝑐ℎ𝑜𝑙𝑒𝑟𝑎 𝑇𝑜𝑡𝑎𝑙 𝑛𝑜.𝑜𝑓 𝑐𝑎𝑠𝑒𝑠 𝑜𝑓 𝑐ℎ𝑜𝑙𝑒𝑟𝑎 X 100 38
  39. 39. Total no. of cholera cases 39
  40. 40. No. of people died due to cholera 40
  41. 41. Total no. of cholera cases 41
  42. 42. Survival rate • Used in research studies • Like cancer therapy or survival = 𝑃𝑎𝑡𝑖𝑒𝑛𝑡𝑠 𝑎𝑙𝑖𝑣𝑒 𝑎𝑡 𝑡ℎ𝑒 𝑒𝑛𝑑 𝑜𝑓 5 𝑦𝑒𝑎𝑟𝑠 𝑇𝑜𝑡𝑎𝑙 𝑛𝑜.𝑜𝑓 𝑝𝑎𝑡𝑖𝑒𝑛𝑡𝑠 X 100 42
  43. 43. What is standardization? You: My salary has doubled this month Ur friend: My salary has also doubled 43 
  44. 44. What is standardization? ¥. 1 Lakh = Rs. 10 Lakh ¥. 2 Lakh = Rs. 20 Lakh Gain = Rs. 10 Lakh Rs. 1 Lakh Rs. 2 Lakh Gain = Rs. 1 Lakh 44
  45. 45. What is standardization? Rs. 1 Lakh = $ 1,500 ¥. 1 Lakh = $ 15,000 Rs. 2 Lakh = $ 3,000 ¥. 2 Lakh = $ 30,000 Gain = $ 1,500 Gain = $ 15,000 45
  46. 46. What is standardization? You: My salary has doubled this month Ur friend: My salary has also doubled 46 
  47. 47. Direct standardization 47
  48. 48. Crude rates Madurai Population Deaths Death rate per 1000 0-64 53,500 446 8.3 Chennai Population Deaths Death rate per 1000 0-64 92,000 850 9.2 48
  49. 49. Age specific rates Madurai Population Deaths Death rate per 1000 0-24 21,500 123 5.7 25-64 32,000 323 10.0 Chennai Population Deaths Death rate per 1000 0-24 32,000 150 4.6 25-64 60,000 700 11.6 49
  50. 50. Standard population Standard Population 0-24 156,000 25-64 45,000 50
  51. 51. Standardization for Madurai Standard Population Madurai rates Expected deaths 0-24 156,000 5.7 889 25-64 45,000 10.0 450 Total 201,000 1,339 Age Population Total deaths Standardized crude rate 0-64 201,000 1,339 6.6 ∂ ∂ ∂ ∂ 51
  52. 52. Standardization for Chennai Standard Population Chennai rates Expected deaths 0-24 156,000 4.6 718 25-64 45,000 11.6 522 Total 201,000 1,240 Age Population Total deaths Standardized crude rate 0-64 201,000 1,240 6.1 ∂ ∂ ∂ ∂ 52
  53. 53. Standardized rates Madurai Population Deaths CDR per 1000 Std. DR per 1000 0-64 53,500 446 8.3 6.6 Chennai Population Deaths CDR per 1000 Std. DR per 1000 0-64 92,000 850 9.2 6.1 53
  54. 54. Indirect standardization 54
  55. 55. Standardized mortality ratio Age National death rate per 1000 25-34 3 35-44 5 45-54 8 55-64 25 55
  56. 56. Standardized mortality ratio Age Doctor population Observed deaths 25-34 300 * 35-44 400 * 45-54 200 * 55-64 100 * Total 1000 9.0 Crude death rate for doctors is 9.0 per 1000 56
  57. 57. Standardized mortality ratio Age National rate Doctor population Observed deaths Expected deaths 25-34 3 300 * 0.9 35-44 5 400 * 2.0 45-54 8 200 * 1.6 55-64 25 100 * 2.5 Total 1000 9.0 7.0 57
  58. 58. Standardized mortality ratio SMR = Observed deaths Expected deaths X 100 SMR = 9/7 X 100 = 129 It means doctors experience 29% more mortality than the general population 58
  59. 59. Summary • There are various measures of mortality • Each one has its own purpose and disadvantages • Standardization is a method for making rates comparable between regions 59
  60. 60. MEASUREMENT OF MORBIDITY 60
  61. 61. Measurement of morbidity • Incidence – Occurrence of new cases • Prevalence – Existence of new and old cases • Incidence – how many people with the disease are newly diagnosed each year (like video) • Prevalence - how many people in a population currently have the disease (like snapshot) 61
  62. 62. Incidence (நடக்குறது) 62 = No. of 𝐍𝐄𝐖 cases of a disease in a particular time period Total population at risk during the same time period X 1000
  63. 63. Incidence – example JANUARY 1, 2016 DECEMBER 31, 2016 63
  64. 64. Special incidence rates • Attack rate • Secondary attack rate 64
  65. 65. Uses of incidence rate • For taking action to control disease • More suited for acute or infectious conditions • For research 65
  66. 66. Example of use of incidence This news article is giving only the numerators, Without denominator, it is hard to place much importance 66
  67. 67. Example of use of incidence 67
  68. 68. Points to remember about incidence • Refers only to new cases • Not influenced by duration of disease • Refers to a particular time period • Denominator is people at risk 68
  69. 69. Prevalence (இருக்குறது) = No.of 𝐎𝐋𝐃 𝐚𝐧𝐝 𝐍𝐄𝐖 cases of a disease in a particular time point/period Total population at risk during the same time period X 1000 69
  70. 70. Types of prevalence • Point prevalence • Period prevalence 70
  71. 71. Point prevalence – example JANUARY 1, 2016 DECEMBER 31, 2016 71
  72. 72. Period prevalence – example JANUARY 1, 2016 DECEMBER 31, 2016 72
  73. 73. Prevalence increases • Longer duration of disease • Prolongation of life with treatment • Increase in incidence • Immigration of new cases • Better reporting of cases • Emigration of healthy people 73
  74. 74. Prevalence decreases • Shorter duration of diseases • Improved cure rate • Decrease in incidence • Emigration of new cases • Under reporting of cases • Immigration of healthy people 74
  75. 75. Uses of prevalence • Magnitude of disease problems • Identify potential high-risk populations • Administrative and planning purposes, e.g., hospital beds, manpower needs, rehabilitation facilities 75
  76. 76. Example of use of prevalence 76
  77. 77. Example of use of prevalence 77
  78. 78. Points to remember about prevalence • Refers to new and old cases • Influenced by duration of disease • Refers to a particular time period • Denominator is people at risk 78
  79. 79. Relation between incidence & prevalence 79
  80. 80. Relation between incidence & prevalence • Prevalence = Incidence X duration • Incidence = 10 cases/1000 population/year • Mean duration of disease = 5 years • Prevalence = 10 x 5 = 50 per 1000 population 80
  81. 81. Summary • Incidence and prevalence are finer measurements of health as compared to death rates • They help us to measure the effectiveness of disease control measures 81
  82. 82. Take home messages • Proportion, rate and ratio – basic tools • CDR is a simple measure of death/health • Standardization is needed for comparability • Incidence reflects new cases only • Prevalence reflects new and old cases • Incidence and prevalence are related • Mortality measures are important, morbidity measures give a better idea of health 82
  83. 83. Review 1 • It was reported that the incidence of dengue was increasing every year in Madurai. This could mean all EXCEPT, a) Control of mosquitoes has failed b) Reporting of dengue cases has improved c) Treatment for dengue has failed d) Public awareness on dengue has increased 83
  84. 84. Review 2 • Prevalence of Diabetes is increasing every year in India. This could mean all EXCEPT, a) Incidence of DM is increasing b) Reporting of diabetes has increased c) Diabetic patients are surviving longer due to better treatment d) Public awareness on diabetes has increased e) None of the above 84
  85. 85. Review 3 • Examples of a disease with high incidence but low prevalence include (multiple options) a) Acute respiratory infection b) Acute diarrhoea c) TB d) Leprosy 85
  86. 86. Review 4 • Examples of a disease with low incidence but high prevalence include (multiple options) a) Acute respiratory infection b) Acute diarrhoea c) TB d) Leprosy 86
  87. 87. Review 5 • A new diabetes control programme was introduced in Madurai. After 1 year, the incidence and prevalence of Diabetes increased. This means a) The programme did not work b) The programme worked c) Data not sufficient 87
  88. 88. Review 6 • Disadvantages of crude death rate include (multiple options) a) Simple measure b) Influenced by the age composition c) Not comparable between countries d) All of the above 88
  89. 89. Review 7 • Proportional mortality is useful for all EXCEPT a) Understanding relative importance of diseases as a cause of death b) Determining measures for reducing preventable mortality c) Indicating the risk for population from dying due to a particular cause d) All of the above 89
  90. 90. Review 8 • Standardized rates can be calculated for a) Age b) Sex c) Race d) Literacy rate e) All the above 90
  91. 91. Review 9 • Standardized mortality ratio requires all EXCEPT a) Age specific denom. for interest pop. b) Age specific death rates for standard pop. c) Age specific death rates for interest pop. d) Crude death rate in interest pop. 91
  92. 92. Review 10 • A patient with Atherosclerotic heart disease for 7 years developed Acute myocardial infarction last week and died today as a result of myocardial rupture. What is the immediate cause of death? a) Acute myocardial infarction b) Atherosclerotic heart disease c) Cardiac arrest d) Rupture of myocardium 92
  93. 93. Review 11 • Mid year population is not the denominator for (multiple options) a) Age specific death rate b) Cause specific death rate c) Crude death rate d) Proportional mortality rate e) Case fatality rate 93
  94. 94. THANK YOU You can find this presentation on Email your queries to sarizwan1986@outlook.com

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