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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