Methodological Notes – Mortality Module
Updated: January 2019
Concepts and Definitions
Measuring the pattern of mortality in a population is an important aspect of assessing the health status of a population, although death represents only the severest consequence of ill health. The most basic information required is the number of deaths, which when divided by the size of the population, produces the crude death rate, expressed as deaths per 1000 persons.
Crude death rate = (number of deaths during year X) / (mean population of year X)Because infancy, defined as age under 1 year, is a particularly vulnerable period in a person’s life, the number of infant deaths is recorded, from which the infant mortality rate (IMR) is constructed, expressed as deaths per 1000 livebirths. IMR is widely used in international comparisons.
Infant mortality rate = (number of deaths under 1 year of age during year X) / (number of livebirths during year X)The rate is Among infant deaths during year X, some were born in year (X-1), and among livebirths in year X, some may go on to die in year (X+1). Some statistical agencies can track a cohort of newborn infants for one year after birth using electronic data linkage between birth and death databases.
Examining the causes of death provides more detailed information on the relative importance of different health problems. Because populations differ in their age-sex composition, and death is very much age-dependent, simple comparisons of crude death rates among populations can be misleading. A more meaningful comparison utilizes age-standardized mortality rates (ASMR). ASMRs adjust for differences in the age distribution of the population by applying the observed age-specific mortality rates for each population (the study population) to a standard population, referred to as the “direct” method:
Age-standardized mortality rate = Σ(ri Ni) / ΣNi
Where ri is the age-specific mortality rate for the ith age group of the study population
Ni is the number of persons in the ith age group of the standard populationThe rate is usually expressed as deaths per 100000 persons. Any population can serve as a standard. When comparing regions within a country, the national population tends to be used as the standard. For international comparisons, there are hypothetical or artificially constructed populations. For ASMR, the standard population used in CircHOB is the European Standard Population (ESP) used by Eurostat until 2013, when it changed the number of people in each age group, which adds up to 100000. CircHOB continues to use the pre-2013 ESP to ensure comparison with previous years’ data without re-calculating all rates. Note that the World Standard Population of the International Agency for Research on Cancer (IARC) is used for computing age-standardized cancer incidence rates.
The age distribution of the European Standard Population is as follows:
| Age group | Population |
|---|---|
| 0-4 | 8, 000 |
| 5-9 | 7, 000 |
| 10-14 | 7, 000 |
| 15-19 | 7, 000 |
| 20-24 | 7, 000 |
| 25-29 | 7, 000 |
| 30-34 | 7, 000 |
| 35-39 | 7, 000 |
| 40-44 | 7, 000 |
| 45-49 | 7, 000 |
| 50-54 | 7, 000 |
| 55-59 | 6, 000 |
| 60-64 | 5, 000 |
| 65-69 | 4, 000 |
| 70-74 | 3, 000 |
| 75-79 | 2, 000 |
| 80-84 | 1, 000 |
| 85+ | 1, 000 |
| Total | 100, 000 |
Source: Eurostat (2013). Revision of the European Standard Population. Annex C shows the pre-2013 age distribution. https://ec.europa.eu/eurostat/en/web/products-manuals-and-guidelines/-/KS-RA-13-028
The causes of death are coded according to the International Classification of Diseases, 10th edition (ICD-10). This is a system of alphanumeric codes, organized into chapters (I to XX). http://apps.who.int/classifications/icd10/browse/2016/en
CircHOB computes and presents ASMRs for several important groups of causes at the ICD-10 chapter level
| All Causes | A00-Y89 [Chapters I-XX] |
| Neoplasms | C00-D48 [Chapter II] |
| Diseases of the Circulatory System | I00-I99 [Chapter IX] |
| Diseases of the Respiratory System | J00-J99 [Chapter X] |
| Injury | V01-Y89 [Chapter XX] |
A widely used health indicator is life expectancy at birth (LE0) which summarizes the mortality experience of a population that prevails across all age groups. It can be defined as the average number of years that a newborn is expected to live if current mortality rates continue to apply. Life expectancy can be computed for other ages, eg. at age 65. The computation of LE is complex, and requires the construction of a life table consisting of the probability of dying, the death rate and the number of survivors for each age or age group. LE at birth is heavily influenced by the extent of deaths among infants and the very young, but is not affected by the different age structures of the populations being compared.
Life tables using 5-year intervals of data (except <1 and 1-4 years) are termed abridged life tables. CircHOB uses the templates for computing abridged life tables described in Toson B, Baker A. Life Expectancy at Birth: Methodological Options for Small Populations, United Kingdom Office of National Statistics, National Statistics Methodological Series No.33, 2003. www.ons.gov.uk/ons/guide-method/method-quality/specific/gss-methodology-series/index.html
Data Sources and Limitations
All statistical agencies maintain mortality databases which contain information relating to the number and causes of death and also basic demographic data of the decedents. As the ages of the decedents are not known in all deaths, the sum of all deaths with known causes is generally less than the total number of deaths.
For data on population age distribution used in calculating crude, age-specific and age-standardized mortality rates, refer to the Population Module in CircHOB. Data on livebirths for use in calculating infant mortality rates can be found in the Fertility Module, unless otherwise specified.
