Community Medicine - LECTURE 3 - Measures of Mortality.pdf

Lecture 3 Measures of Population Health Status II: Mortality + Mortality Application SEITE 1  Quick Review Measures of occurrence/frequency Of morbidity = dise...

Lecture 3 Measures of Population Health Status II: Mortality + Mortality Application SEITE 1  Quick Review Measures of occurrence/frequency Of morbidity = disease Of mortality = death Measures of association SEITE 2  Why Do We Look at Mortality Data? Everybody eventually dies A good measure of community health Data about mortality are regularly collected Data on all-cause mortality are valid (hard endpoint) Death as a measure of disease severity is an important event Compare between groups Identify opportunities for prevention Identify opportunities to improve overall health of communities SEITE 3  Three Major Sources of Mortality Data 1- Death Certificates: Provide information on: a- Number of deaths b- Characteristics like age, sex, race, etc. c- Causes of death (underlying cause of death using the International Classification of Diseases (ICD-codes): “the disease or injury that initiated the chain of morbid events that led directly and inevitably to death” [CDC, 2004],) SEITE 4  Three Major Sources of Mortality Data 2- Certificate of fetal death: It is required for all deaths “prior to the complete expulsion or extraction from its mother of a product of human conception, irrespective of the duration of pregnancy and which is not an induced termination of pregnancy.” [WHO, 1950] 3- Maternal death: “The death of a woman while pregnant or within 42 days of termination of pregnancy, irrespective of the duration and the site of the pregnancy, from any cause related to or aggravated by the pregnancy or its management, but not from accidental or incidental causes.” Mortality data from all sources are gathered at local or regional levels → national level (National Death Index) SEITE 5  Crude Mortality Rate Crude rates are rates that apply to an entire population, without taking in account any characteristics of the individual (e.g. age) Crude death rate (CDR) = Number of deaths among residents in an area in a calendar year X K Mid-year population in this area in that year Two factors contribute to the magnitude of a CDR: a. The probability of dying for individuals b. The age distribution of the population Example: In a city of 100,000 inhabitants the total deaths in 1995 was 500 person calculate CDR per 1000 population CDR = 500 X 1000 = 5 / 1000 100000 SEITE 6  Specific Mortality Rates Crude rates can not be used comfortably to make comparisons between populations. Therefore, detailed rates specific for age and other demographic components, such as sex or race, are sometimes needed. Age specific death e.g. ages 25-34 = Number of deaths among residents aged 25-34 in an area in a year X K Mid-year population aged 25-34 in the area in that year Infant mortality rate (IMR) = Number of deaths among infants (< 1 year) in a year X K Total number of live births in the same year Maternal mortality rate (MMR) = Number of maternal deaths in a year X 1,000 Total number of live births in the same year SEITE 7  Specific Mortality Rates Sex specific death (mortality) rate Male specific death rate = Number of deaths among males in an area in a calendar year______ X K Mid-year population of males in that year Cause-specific mortality rate = Deaths assigned to a specified disease (cause) during a calendar year X K Mid-year population Example: in a city of 100,000 inhabitants 40 deaths occurred from T.B. Calculate T.B. cause specific mortality rate per 100000 of population T.B. cause- specific mortality rate = 40 X 100000 = 40 / 100,000 100000 SEITE 8  Case Fatality Rates (CFR) Number of individuals dying during a specified period of time after a disease onset or diagnosis X K Number of individuals with the specified disease during the same period In CFR, the constant is usually "100" (but it may differ according to the problem) EXAMPLE: In a city during the year 2005, 100 cases of meningitis occurred, and death occurred among 15 of these case. Calculate the CFR Case fatality rate (CFR) of meningitis = 15 X 100 = 15 % 100 Importance of CFR: a- It represents the risk of dying during a definite period of time for those individuals who have the particular disease b- CFR is a useful measure for severity of the disease (it measures the pathogenicity and virulence of the disease) SEITE 9  Proportionate Mortality Number of deaths from a given cause (disease) in a specific time period __ X K Total number of deaths in the same time period from all causes K is usually 100 (but may be other according to the problem) Importance of proportionate mortality : a- It represents the proportion of total deaths that are due to a specific cause b- It tells us about the relative importance of a specific cause of death in relation to all deaths in a population SEITE 10  Adjusted or Standardized Mortality Rate Standardization is used to remove the effect of an unwanted variable, such as age, from a comparison between two populations Variables to be adjusted for may include age (most important), sex, race, smoking status, etc. There are two methods of adjustment: (1) The direct method (2) The indirect method We will use them to calculate a standardized mortality rate or standardized mortality ratio SEITE 11  Steps for Direct Standardization Suppose that there are two populations A, B and we need to do standardization Calculate crude (observed) mortality rate for each of the two population: Total number of deaths X K Total population Develop a standardized population; one population only instead of 2, e.g. by summation of Pop. A + Pop. B ( in each stratum (each row) and for the total population). Calculate the age-specific expected number of deaths in the standard population by multiplying death rate of each age group by the standard population =Death rate for each age group X Standard population (A+B) Calculate the expected number of deaths for each age group and for both populations separately Calculate the total expected number of deaths for each population separately Calculate the Standardized Mortality Rate for each population as following: Standardized Mortality Rate = Total expected number of deaths XK Total number of persons in the standardized population (A+B) Compare the standardized mortality rates of the two populations SEITE 12  Example for Direct Standardization Calculate age specific & CRUDE death rate in community A and B: Community A Community B Death rate (per Death rate (per Age (year) Population Deaths Population Deaths 1000) 1000) 15 X 1000 = 100 X 1000 = 1000 5000