By:Dr.Yossra K.Al-Robaiaay Assistant professor FICMS (FM) Measures of mortality By:Dr.Yossra K.Al-Robaiaay Assistant professor FICMS (FM)

A mortality rate is a measure of the frequency of occurrence of death in a defined population during a specified period of time.

Measures of mortality Mortality is clearly an index of the severity of the problem from both clinical and public health standpoints. Mortality can also be used as an index of the risk of the disease. Most of our information about deaths comes from death certificate. Deaths are coded according to the underlying causes. Analysis of mortality information depends on the quality of the data included.

The Mortality Rates   A mortality rate is a measure of the frequency of occurrence of death in a defined population during a specified period of time.

How is mortality expressed in quantitative terms? Annual crude mortality rate: = All deaths during calendar year / Total mid year population*1000 Ex: In a population of 2 million, the total reported deaths from all causes were 12000 in 1995. The annual crude mortality rate in that year per 1000 persons was: 12000/2000000 X 1000 = 6 per 1000 population per year. ((The crude death rate is the starting point for further development of adjusted rates)).

It is important to use the population size at the midpoint of the time interval as an estimate of the average population at risk especially if a denominator population is growing or shrinking during the period of time for which a rate is to be computed. e.g. If a death rate is to be calculated for the year 2000, then the population of July 1, 2000 is used for the denominator.

Proportionate mortality ratio: = Total number of deaths due to a certain disease / Total number of deaths from all causes * 1000 Ex: There were 6000 deaths (1200 leukemia, 1750 stroke, 250 pneumonia, 250 Hodgkin's disease, 2500 acute myocardial infarction, and 50 others) in certain community which had a population of 2.5 million populations in 1996. The Proportionate mortality rate for leukemia is: = 1200 /6000 X 1000 = 20%

Age (sex, race…..) specific mortality rate:

Cause specific mortality rate: = Number of deaths due a specific disease/ Total mid year population*1000 Ex: There were 6000 deaths (1200 leukemia, 1750 stroke, 250 pneumonia, 250 Hodgkin's disease, 2500 acute myocardial infarction, and 50 others) in certain community which had a population of 2.5 million populations in 1996. The cause specific mortality rate for acute MI in this population was: =2500/2'500'000X1000=1 per 1000  

Case fatality rate: (Usually express in percentage) = Number of deaths due to specific disease/ Number of people with the same disease*100 (Usually express in percentage) Ex: In a city, there were 500 HIV- positive people of whom 5 died within a year after their initial diagnosis. The case fatality rate is = 5/500 X100= 1%. Note: The ''survival rate'' in that year was 99%(100%-1%)

Comparison of a mortality rate and case fatality rate: Assume a population of 100'000 people of whom 20 are sick with disease ''X'', and in 1 year, 18 die from that disease. The mortality rate in that year from disease x = 18/100000= 0.018%. The case fatality rate from disease x = 90/100= 90%.

Number of infant (< 1 year) deaths mortality rates: Some special Infant mortality rate Number of infant (< 1 year) deaths mortality rates: Number of live births Neonate mortality rate Number of neonate (≤ 28 days) deaths   Perinatal mortality rate Number of stillbirths + deaths in 1st week of life Total births Stillbirth rate Number of intrauterine deaths after 28 weeks Maternal mortality rate** (usually per 100,000) Number of deaths among women due to after 28 weeks NB These rates are usually related to one year

2. Age (sex…..category) -specific mortality rate An age-specific mortality rate is a mortality rate limited to a particular age group. The numerator is the number of deaths in that age group(or any category) The denominator is the number of persons in that age group or category in the population.

Sex-specific mortality rate A sex-specific mortality rate is a mortality rate among either males or females. Both numerator and denominator are limited to the one sex.  

Infant mortality rate: No. of infants dying under one year of age in a year per thousand live birth in a given geographical region. D0 : No. of infants who died before completing their first year. B : Total No. live births occurring in that year and geographical region. D0 B  1000 IMR=

Neonatal Mortality Rate (NMR): No. of infants dying within the first 4 weeks or up to 28 days of life per 1000 live birth in a year and geographical region. NMR = Deaths of infants up to 4 weeks No. of live births × 1000 Early Neonatal Mortality Rate (NMR): No. of infant deaths during the first seven days of life per 1000 live births in a year and geographical region. ENMR = Deaths of infants in the first week of life No. of live births × 1000

Post Neonatal Mortality Rate (PNMR) Number of infants deaths after 28 days to less than 1yr (between 4 weeks to 52 weeks) of age per 1000 live births in a given year. PNMR= No. of deaths of newborns between 4weeks or less than 1yr old in a year No. of live births during the same yr × 1000

Maternal Mortality Ratio (MMR) No. of deaths of women while pregnant or within 42 days of termination of pregnancy from any cause related to pregnancy/ childbearing and child birth per 100,000 live births in a given year. No. of live births during the same year × 100000 MMR= Deaths of pregnant women and women after termination of pregnancy within 6 weeks from any cause related to pregnancy

Maternal Mortality Rate (MMRT) Number of maternal deaths while pregnant or within 42 days of termination of pregnancy from any cause related to pregnancy/ childbearing and childbirth per 100,000 women in reproductive ages 15-49. No. of maternal deaths of women in age 15-49 × 1000 MMRT = No. of women in age 15-49 in a given yr

Foetal Death: Deaths prior to the complete expulsion or extraction from its mother of a product of conception at any time of pregnancy. Still Birth Death of foetus after completing 28 weeks and till the time of birth.

Time Reference for Mortality in Childhood and Infancy 28 weeks of gestation completed Live Birth 7 Days 28 Days 1 Year 5 Years Still Birth Neonatal Early Death Late Post Toddler Perinatal Death Infant Death Child Death (<5 Years)

Limitations of Measures of Mortality The risk in a population may vary largely with various socio-economic and biological traits. The lack of reliable and requisite data presents serious problem sometimes of considerable magnitude.

6. Maternal mortality rate (ratio) The maternal mortality rate is really a ratio used to measure mortality associated with pregnancy. The numerator is the number of deaths assigned to causes related to pregnancy during a given time period. The denominator is the number of live births reported during the same time period. Because maternal mortality is much less common than infant mortality, the maternal mortality rate is usually expressed per 100,000 live births. In 1988, the maternal mortality rate was 8.4 per 100,000 live births.

Combinations of specific mortality rates Different combinations of specific mortality rates can be calculated e.g. cause-specific, age-specific,… For example, the mortality rate attributed to HIV among 25- to 44-year-olds in the United States in 1987 was 9,820 deaths among 77.6 million 25- to 44-yearolds, or 12.7 per 100,000. This is a cause- and age-specific mortality rate, because it is limited to one cause (HIV infection) and one age group (25 to 44 years).

Rates whose denominators are total population: Crude mortality rate (crude death rate) Crude Birth rate (crude Birth rate) Cause-specific mortality rate

Rates whose denominators are total population: Infant mortality rate Neonatal mortality rate Postneonatal mortality rate Maternal mortality rate

 Exersice 1: A total of 2,123,323 deaths were recorded in the United States in 1987. The mid-year population was estimated to be 243,401,000 calculate Crude mortality rate.

 Exersice 1: A total of 2,123,323 deaths were recorded in the United States in 1987. The mid-year population was estimated to be 243,401,000 calculate Crude mortality rate. All deaths during calendar year / Total mid year population*1000 Crude mortality rate= 2,123,323/ 243,401,000 *1000 =8.7 per 1000

Exercise 2: -In 2008 a total of 12,088 TB-related deaths occurred in males and 1,380 TB-related deaths occurred in females. The estimated 2008 midyear population for males and females was 118,531,000 and 124,869,000, respectively. a. Calculate the TB-related death rate for males and for females. b. What type of mortality rates did you calculate in step a? c. Calculate the TB-mortality rate ratio for males versus females

a. TB -related death rate for males = (12,088/118,531,000) × 100,000 = 10.2 per 100,000 HIV-related death rates for females = (1,380/124,869,000) × 100,000 = 1.1 per 100,000 b. These rates are cause-specific and sex-specific mortality rates c. TB -mortality rate ratio for males versus females =(10.2 per 100,000) / (1.1 per 100,000) = 9.3 HIV-related mortality rate was 9.3 times higher for males than for females.

Exercise 3: From table Calculate HIV (cause)-specific mortality rate for the entire population calculate HIV-related mortality rate among 35- to 44-year-olds (cause-specific and age-specific mortality rate) in all races

HIV –related mortality rate for the intire population = (13,468/243,401) × 1000 = 55.3 per 1000 b. HIV-related mortality rate among 35- to 44-year-olds (cause-specific and age-specific mortality rate) in all races =(4,794/34,305) × 1000 = 139.7 per 1000

: Exersice 4 : in 2001, a total of 15,555 homicide deaths occurred among males and 4,753 homicide deaths occurred among females. The estimated 2001 midyear populations for males and females were 139,813,000 and 144,984,000, respectively. 1-Calculate the homicide-related death rates for males and for females. 2-What type(s) of mortality rates did you calculate in Question 1? 3-Calculate the ratio of homicide-mortality rates for males compared to females. Interpret the rate you calculated in Question 3 as if you were presenting information to a policymaker.

a. Homicide-related death rate for males = (15,555/139,813,000) × 100,000 = 11.1 per 100,000 Homicide-related death rate for females = (4,735/144,984,000) × 100,000 = 3.3 per 100,000 b. These rates are cause-specific and sex-specific mortality rates c. Homicide-related death ratio for males versus females =(11.1 per 100,000) / (3.3 per 100,000) = 3.4 Homicide-related death rate was 3.4 times higher for males than for females.

Exersice 5: In an epidemic of hepatitis A from a restaurant, 555 cases were identified. Three of the case-patients died as a result of their infections. Calculate the case-fatality rate   Which mortality measurement, can give us idea about the mortality& morbidity at the same time?

= Number of deaths due to specific disease/ Number of people with the same disease*100 (Usually express in percentage) 3/555*100 =0.54%

QUIZ : Calculate the crude death rate and age specific mortality rate among (20-40) years old from the following data Age-group (Years) Population Deaths Under 10 20,000 600 10-20 12,000 240 20-40 50,000 1,250 40-60 30,000 1,050 Above 60 10,000 500 TOTAL 122,000 3,640

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