FINAL TERM COURSE

Measures of Mortality (v) Standardized Death Rates by Direct Method

Standardized Mortality Rate It is a weighted average of the age-sex specific mortality rates of a particular population under observation, the weights being the proportions in each age-sex group of a standard population (not the particular population under observation)

Explanation The crude death rates of two localities or in two occupations cannot be compared because mortality rates differ with age, sex, climate, occupation etc. Aged people even though well housed and well fed, die comparatively at a higher rate than the young people. Good climate is conductive to long life whereas bad climate is injurious to health. Moreover, mortality is highest at the extreme of age. To eliminate such effects, we compute “Standardized death rates”

Methods of calculating SDR Standardized death rates can be computed either by ◦ Direct method: SDR by direct method can be calculated by applying different age-specific death rates of the population being studied (or given population), to a standard population (which may be any population selected to be on the basis of the comparison) ◦ Indirect method: SDR by indirect method can be calculated by applying different age specific death rates of a standard population to the population being studied.

Direct method The direct method for computing the SDR consists in calculating the number of deaths that would be expected to occur in a standard population if the age specific death rates of the given population were to apply; and dividing the sum of the expected deaths by standard population.

That is the age adjusted or standardized death rate is computed by the formula

Where denotes the number of deaths occurring in the given population in the ith age group during a calendar year denotes the mid year population figures in the given population in ith age-group during the same year. denotes the mid year population figure in the standard population in the ith age group in the same year.

If the death rates are adjusted both for age and sex, the expected deaths are calculated as follows:

The standardized death rate or age sex- adjusted death rate is then given by the formula: This sort of SDR is easy to compute and to explain. The choice of standard population being subjective, may influence the comparison of standardized death rates.

Example 1 Given the following data for the two districts: Compute Crude Death Rates for district A and B and interpret by pointing out the fallacies. Considering district A as a standard population, calculate standardized death rate for district B using direct method.

Data Table Age group (years) District ADistrict B PopulationDeathsPopulationDeaths & over

Solution The computation of crude death rates and age-specific death rates in both the districts to point out the fallacies, if any, are given below:

Age- group (years) District ADistrict B Populatio n DeathsA.S.D.RPopulatio n DeathsA.S.D.R (2/500)x 1000= & over Total

Calculation of CDR

Calculation of SDR To compute the SDR for district B by the direct method, we first calculate the expected deaths in district A (standard population) as experienced in district B by the formula The deaths are given in the next table

Expected death calculation Age group (years)Expected deaths in standard population as experienced in district A 0-14(1/400)x500 = (1/300)x2000 = & over12 Total57

Hence standardized death rate is:

Interpretation The CDR for district B, which contains a very large proportion of older people. i.e. 72% of district B’s population is over the age 45 years, comes to 23.8 unusually high, whereas the CDR for district A, which contains a smaller proportion of older people i.e. only 26% population is over age 45 years, is 11.0, unusually low.

Interpretation The death rate at all age groups in district B are lower than those in district A but the CDR of B is more than double the CDR of A. The fallacy this sort of unusual behavior lies in the fact that the like is not being compared with the like. For such situation SDR are calculated. Standardizing has lowered the death rate for district B, which turn out to be 9.3

Mathematical formula of SDR Ref. Benjamin B. & Pollard J.H. (1980), “The Analysis of Mortality and Other Actuarial Statistics”, William Heinemann Ltd The Direct Standardized Death Rate can be calculated as: where is the standard population.

Example Ref. Benjamin B. & Pollard J.H. (1980) The data are available for males in two areas A & B and for the whole country C a.Calculate the death rate by age for each area. b.Also calculate CRD c.Standardize the all ages death rates for area A and B directly by reference to the population of C d.Interpret all the findings.

Data Table Population (000s)Annual deaths (all causes) AgeABCABC

Solution (a) Values of AgeArea AArea B /150000=

(b) Calculation of CDR (?)

Solution (c), Answers Standardized death rate for area A= Standardized death rate for area B=0.0193

(d) Interpretation (?)