Session 4.2 Mortality and Morbidity Rates Age Adjustment

Transcription

1 Session 4.2 Mortality and Morbidity Rates Age Adjustment

2 Crude mortality rate = All deaths in a calendar year Population at mid year 1000 This crude rate expresses the actual observed mortality rate in a population under study for a given population

3 Mortality and Age Age is the most important characteristic governing mortality. Before the experience of mortality in two populations can be compared, account must be taken of differences in age composition.

4 Age-Specific Mortality Rates Mortality rates per 1,000 population by age and race in Baltimore City. All ages < 1 yr White Black The population of Baltimore City consists of old whites and young blacks.

5 Mortality rates based on age structure Community A 1/2 young people & 1/2 old people. Community B 2/3 young people and 1/3 old people The age-specific death rates in the communities /1,000 are: Community Young Old A 4 16 B 5 20

6 The crude mortality rates Mortality rate for A = (1/2)(4) + (1/2)(16) = 10 per 1,000 Mortality rate for B = (2/3)(5) + (1/3)(20) = 10 per 1,000

7 Confounding Occurs whenever a third factor affects the outcome in addition to the factor under study (disease, age, and mortality). The effect of the confounder can be removed using statistical adjustment during analysis.

8 Use of population structure of community B Age-adjusted mortality rate for A = (1/3)(4) + (2/3)(16) = 12 per 1,000 Age-adjusted mortality rate for B = (1/3)(5) + (2/3)(20) = 15 per 1,000

9 Age groups World standard European standard WHO World Standard Total

10 Age-adjusted Mortality Rates Mortality Rates Population A (Disease & Age Structure) Mortality Rates Population B WHO Standard Population Adjusted Rates Population A (Disease only) Comparison Adjusted Rates Population B

11 Other measures of mortality Sex-, Race- and Cause-specific Mortality Rates: Same definitions for a specific, sex, and cause Proportionate Mortality ratio: Number of deaths from a given cause expressed as proportion (%) from total deaths. Case-fatality rate: No.of deathsdue to the diseasein a specifiedtimeperiod 100 No.of casesof the diseasein the sametimeperiod

12 Morbidity Measures Crude Incidence Rate = New Cancer Cases Midyear Population 100,000 Prevalence Rate = Existing Cancer Cases Midyear Population 100,000

13 Age-adjusted Incidence Rates Incidence Rates Population A (Incidence & Age Structure) Incidence Rates Population B WHO Standard Population Adjusted Rates Population A (Incidence only) Comparison Adjusted Rates Population B

14 Prevalence Prevalence depends on two factors; the incidence the duration of disease. Prevalence = Incidence x Duration Thus, a change in disease prevalence may reflect a change in Incidence, Outcome, or both.

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16 For example If improvements in therapy preventing death not producing recovery may give rise to increase in prevalence of the disease. A decrease in prevalence may result decrease in incidence shortening of the duration of disease more rapid recovery or more rapid death.

17 A city with 100,000 people. 45,000 males, 55,000 females person die per year; 600 males and 400 females. 50 cases of lung cancer per year; 40 males and 10 females. Of whom 45 died; 36 males and 9 females. Calculate Crude mortality rate No. of deaths within a certain locality and year Mid year population in the same locality and year , = 10 deaths per

18 A city with 100,000 people. 45,000 males, 55,000 females person die per year; 600 males and 400 females. 50 cases of lung cancer per year; 40 males and 10 females. Of whom 45 died; 36 males and 9 females. Calculate Sex-specific mortality rate No. of male deaths within a certain locality and year Mid year male population in the same locality and year , = Males deaths per 1000 males

19 A city with 100,000 people. 45,000 males, 55,000 females person die per year; 600 males and 400 females. 50 cases of lung cancer per year; 40 males and 10 females. Of whom 45 died; 36 males and 9 females. Calculate Sex-specific mortality rate No.of female deaths within a certain locality and year 1000 Mid year female population in the same locality and year ,000 Females 1000 = 7.3 deaths per 1000 females

20 A city with 100,000 people. 45,000 males, 55,000 females person die per year; 600 males and 400 females. 50 cases of lung cancer per year; 40 males and 10 females. Of whom 45 died; 36 males and 9 females. Calculate Cause-specific mortality rate for lung cancer No. of deaths due to lung cancer within a certain locality and year Mid year population in the same locality and year , = 0.45 deaths per 1000

21 A city with 100,000 people. 45,000 males, 55,000 females person die per year; 600 males and 400 females. 50 cases of lung cancer per year; 40 males and 10 females. Of whom 45 died; 36 males and 9 females. Calculate Case fatality rate for lung cancer No. of deaths due to lung cancer in a specified time period 100 Total No. of cases of lung cancer in the same time period = 90% 50

22 A city with 100,000 people. 45,000 males, 55,000 females person die per year; 600 males and 400 females. 50 cases of lung cancer per year; 40 males and 10 females. Of whom 45 died; 36 males and 9 females. Calculate Proportionate mortality rate (PMR) for lung cancer No. of deaths due to lung cancer in a specified time period 100 Total No. of deaths in the same time period = 4.5% 1000

23 There were 2,448,288 deaths in United States in What is the additional information required to compute the crude mortality rate? No. of deaths within a certain locality and year Crude mortality rate = 1000 Mid year population in the same locality and year So, we need the midyear population of the US in 2003, which equals = 295,734,134 2,448, ,734, = 8.25 deaths per 1000

24 In 2003, crude mortality rate In Mexico was 4.83/1000. In US, it was 8.25/1000. Can the lower crude mortality rate be explained by the fact that the United states has a larger population? Explain No, because the mortality rate refers to the No. of deaths per 1000 population in both countries.

25 In 2003, crude mortality rate In Mexico was 4.83/1000. In US, it was 8.25/1000. Give the most probable explanation of the lower crude mortality rate in Mexico In Mexico High-age specific death rate in the first decades Relatively younger population Relative deficiency of old people Thus, the crude mortality rate is low despite high-age specific mortality rate because of smaller proportion of elderly person

26 Crude mortality rate from heart diseases In US was In Chile it was 67.4 What is the ratio? 316.3/67.4 = 4.7 BUT the age-adjusted mortality rate from heart diseases In US was In Chile it was 58.2 So, the ratio is 131.4/58.2 = 2.3 Which of the two rates is Preferable for comparison? Age-adjusted is preferable because age composition effect is removed by adjustment

27 INCIDENCE AND PREVALENCE

28 t1 t2 8 ill patients 1 T1 = beginning of a year 2 T2 = end of a year Population = 20 persons 4 3 Calculate 5 Incidence during this year 6 o. of new cases of the disease 100 Population at risk = 20% Jan 1 Dec 3

29 t1 t2 8 ill patients 1 T1 = beginning of a year 2 T2 = end of a year Population = 20 persons 4 3 Calculate 5 Point prevalence at t1 6 o. of total cases of the disease 100 Population at risk = 20% Jan 1 Dec 3

30 8 ill patients 1 T1 = beginning of a year 2 T2 = end of a year Population = 20 persons 4 3 Calculate 5 Point prevalence at t2 6 7 o. of total cases of the disease 100 Population at risk = 15% Jan 1 Dec 3

31 8 ill patients 1 T1 = beginning of a year 2 T2 = end of a year Population = 20 persons 4 3 Calculate 5 Period prevalence during the year (t1-t2) 6 7 o. of old and new cases of the disease 100 Population at risk = 40% Jan 1 Dec 3

32 t1 t2 8 ill patients 1 T1 = beginning of a year 2 T2 = end of a year Population = 20 persons 4 3 Calculate 5 Incidence Point prevalence at beginning and at end Period prevalence during the shaded period Jan 1 Dec 3

33 Epilepsy Multiple sclerosis Parkinson's disease Motor neuron disease CNS neoplasms Rates per 100,000 population Prevalence 9 80 Incidence compute the average duration, in years, of the five chronic neurological conditions listed Prevalence = Incidence x Duration Duration of epilepsy = 360/30 = 12 Duration of MS = 55/5.0 = 11 Duration of PK = 160/20 = 8 Duration of ND = 9/1.5 = 6 Duration of Neo = 80/16 = 5

34 Prevalence of coronary heart disease decreases after age 70 Its incidence continues to increase with age. What is the most probable explanation for the divergence of these rates? Patients older than age 70 who develop coronary heart disease have shorter survival times than the younger patients.

35 t1 t years 80 years