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Measures of Morbidity
www.cdc.gov/mmwr
Morbidity and Mortality Weekly Reports
Terms Related to Morbidity
• Morbidity
The extent of illness, injury or disability in a
defined population
• Incidence of...
Characteristics
RISK PREVALENCE INCIDENCE
RATE
Probability of
disease
% of pop. with
the disease
Rapidity of
disease
occur...
Problems with Numerators
• Who has the disease?
• Who to include in numerator?
• Interview errors
Problems with Denominator
• Selective undercounting
• Everyone in denominator must have
potential to enter numerator group
Problems with Hospital Data
• Selective (many reasons)
• Data may be unavailable, etc
Incidence
The two forms of incidence are:
• Cumulative incidence
• "risk of disease“
• measures the proportion of
persons ...
Incidence per 1000
What’s wrong with this formula?
Incidence Rate
• Measures the rapidity with which newly
diagnosed cases of the disease of interest
develop
 observe a pop...
Incidence Rate (Attack Rate) (cont.)
• Can be used for specific exposures
• Also used for multiple exposures
• Other terms...
Principles of Incidence Rate
• Estimate probability
• Incidence kinetics
• Seasonal variation
• Place
• Person
Attack rates
Incidence and Attack Rates
• Primary Attack rates
Incidence and Attack rates
(cont’d)
• Secondary Attack rates
Incidence Rates
OSHA
Prevalence
• Measure of the number (or proportion) of
cases in a given population
• What is the difference between prevale...
Prevalence
• Point prevalence- point in time
• Period prevalence- during a defined
range of time
Comparative Factors
Affecting Prevalence Rates
• Rates are INCREASED by
 Immigration of ill cases
 Emigration of healthy...
Comparative Factors
Affecting Prevalence Rates
• Rates are DECREASED by
 Immigration of healthy persons
 Emigration of i...
Prevalence Rates
Prevalence Rates
• Point
• Period
(cont’d)
Rates of Morbidity
Breast Cancer Incidence in White Women and
Distribution by Age
Note change in slope –
menopause??
Case Distribution
Spot Map of Residence Distribution of
Rheumatic Fever Cases in Baltimore
1960-
1964
1977-
1981
Sources of Morbidity Statistics
• Clinical and hospital
• Managed care
• Registries
• Vital statistics
• Surveys
• Disease...
Lec4 morbidity(revised07)
Lec4 morbidity(revised07)
Lec4 morbidity(revised07)
Lec4 morbidity(revised07)
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Lec4 morbidity(revised07)

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morbidity

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Lec4 morbidity(revised07)

  1. 1. Measures of Morbidity
  2. 2. www.cdc.gov/mmwr Morbidity and Mortality Weekly Reports
  3. 3. Terms Related to Morbidity • Morbidity The extent of illness, injury or disability in a defined population • Incidence of a disease (Incidence rate) The number of new cases of a disease that occur during a specified time period (numerator) in a population at risk for developing the disease (denominator) • Prevalence of a disease (Prevalence rate) The number of total cases of disease present at a particular time (numerator) in a specific population (denominator) • Risk The likelihood that an individual will contract a disease
  4. 4. Characteristics RISK PREVALENCE INCIDENCE RATE Probability of disease % of pop. with the disease Rapidity of disease occurrence No units No units Cases per person-time Newly diagnosed Existing Newly diagnosed “Cumulative incidence” “Incidence density”
  5. 5. Problems with Numerators • Who has the disease? • Who to include in numerator? • Interview errors
  6. 6. Problems with Denominator • Selective undercounting • Everyone in denominator must have potential to enter numerator group
  7. 7. Problems with Hospital Data • Selective (many reasons) • Data may be unavailable, etc
  8. 8. Incidence The two forms of incidence are: • Cumulative incidence • "risk of disease“ • measures the proportion of persons who develop a disease in a known span of time • Incidence rate • "rate of disease“ • measures the rate of new disease occurrence over time
  9. 9. Incidence per 1000 What’s wrong with this formula?
  10. 10. Incidence Rate • Measures the rapidity with which newly diagnosed cases of the disease of interest develop  observe a population  count # of new cases  measure net time • individuals in population at risk of developing disease • person-time  person-years  patient-days
  11. 11. Incidence Rate (Attack Rate) (cont.) • Can be used for specific exposures • Also used for multiple exposures • Other terms: primary case secondary attack • secondary cases
  12. 12. Principles of Incidence Rate • Estimate probability • Incidence kinetics • Seasonal variation • Place • Person
  13. 13. Attack rates
  14. 14. Incidence and Attack Rates • Primary Attack rates
  15. 15. Incidence and Attack rates (cont’d) • Secondary Attack rates
  16. 16. Incidence Rates OSHA
  17. 17. Prevalence • Measure of the number (or proportion) of cases in a given population • What is the difference between prevalence and incidence? Prevalence → a slice thru a population at a given point in time that determines who has the disease and who does not, while Incidence only looks at new cases • In steady state situation (no change in rate or net population) Prevalence = Incidence X Duration of disease
  18. 18. Prevalence • Point prevalence- point in time • Period prevalence- during a defined range of time
  19. 19. Comparative Factors Affecting Prevalence Rates • Rates are INCREASED by  Immigration of ill cases  Emigration of healthy persons  Immigration of susceptible cases or those with potential of becoming cases  Prolongation of life cases w/o cure • Increase of duration of disease Increase in occurrence of new cases • Increase in incidence
  20. 20. Comparative Factors Affecting Prevalence Rates • Rates are DECREASED by  Immigration of healthy persons  Emigration of ill cases  Improved cure rate of cases  Increased death rates from diseases  Decrease in occurrence of new cases  Shorter duration of disease  Death
  21. 21. Prevalence Rates
  22. 22. Prevalence Rates • Point • Period (cont’d)
  23. 23. Rates of Morbidity Breast Cancer Incidence in White Women and Distribution by Age Note change in slope – menopause??
  24. 24. Case Distribution Spot Map of Residence Distribution of Rheumatic Fever Cases in Baltimore 1960- 1964 1977- 1981
  25. 25. Sources of Morbidity Statistics • Clinical and hospital • Managed care • Registries • Vital statistics • Surveys • Disease reporting • Insurance and pre-paid med. care plans • Absenteeism records

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