Epidemiologic Mind : Measurements of Mortality and Crude Death Rate

Epidemiologic Mind : Measurements of Mortality and Crude Death Rate

Mortality rates and ratios measure the occurrence of deaths in a population using different ways. Rates whose denominators are the total population are commonly calculated using either the mid -interval population or the average population. This is done because population size fluctuates over time due to births, deaths and migration.

Below are given some formulas for the commonly used mortality rates and ratios.

1. Crude Death rate (CDR)

The Crude Death Rate measures the proportion of the population dying every year, or the number of deaths in the community, per 1000 population. It reflects the risk of death in that community or country.

Currently the Crude Death Rate in Ethiopia is 12.6 per 1000 population (1995 health & health related indicators, MOH). That means out of 1000 total population about 13 people die each year.

One example of age specific mortality rate is Infant Mortality Rate

Example: The average total population of “Kebele Y” in 1996 was 6000 (3500 female & 2500 male). In the same year 300 people died (100 female & 200 male). Calculate the mortality rate (Crude death rate) for females.

CDR for females = 100/3500 X 1000 = 29 per 1000 female population

That means out of 1000 female population living in “Kebele Y”, 29 females died in 1996.

The proportionate mortality ratio asks the question: What proportion of deaths are due to a certain cause? For example when we say the proportionate mortality ratio for HIV/AIDS is 30 %, this means out of 100 total (of all) deaths 30 of them died from HIV/AIDS.

Case fatality rate represents the probability of death among diagnosed cases or the killing power of a disease.

Example: In 1996 there were 1000 tuberculosis patients in one region. Out of the 1000 patients 100 died in the same year. Calculate the case fatality rate of tuberculosis.

CFR = 100/1000 x 100 = 10 %

That means 10% of tuberculosis patients will die once they develop the disease

Example: In 1996 there were a total of 5000 live births in “Zone B”. Two hundred of them died before 28 days after birth. Calculate the Neonatal Mortality Rate (NMR).

NMR = 200/5000 X 1000 = 40 per 1000 live births

That means out of 1000 live births in 1996, 40 of them died before 28 days after birth.

Death during the neonatal period is largely due to prematurity, malformations, accidents or injuries at birth, and lack of cleanliness and sterility during or after delivery. In addition, it reflects the inadequacy of antenatal care.

Infant mortality rate reflects the health of the community in which the child is being brought up. Thus, it is high among people who have little health care, chiefly because infections, such as pneumonia, diarrhea and malaria, are common among their infants. Malnutrition is also one of the killer of infants in developing countries. The infant mortality rate in Ethiopia is one of the highest in the world (96.8 per 1000 live births). That means out of 1000 live births about 97 die
before they celebrate their first birth day.

NB: The numerator says 0-4 years. 0-4 years in this formula means children from birth to less than five years of age i.e the upper age limit is not 4.

Example: In 1996 the total number of children under 5 years of age was 10,000 in “Zone C”. In the same year 200 children under five years of age died. Calculate the under five-mortality rate (U5MR).
U5MR = 200/10000 x 1000 = 20 per 1000 under five children

That means in “Zone C”, out of 1000 under five children, 20 died in 1996.

Maternal Mortality Rate reflects the standards of all aspects of maternal care (antenatal, delivery and postnatal).

The Maternal

Mortality Rate in Ethiopia is estimated to be 871 per 100,000 live births. That means in 100,000 live births, around 871 mothers die each year due to pregnancy related causes.

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