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Crude death
rate specific death rate standardised death rates. |
VITAL
STATISTICS
Measurement of Mortality. The following are the
principal rates used in measuring mortality.
Crude Death Rate (C.D.R.). This is the simplest of
all the indices of mortality and is defined as the number of deaths (from all
causes) per k persons in the population of any given region or community during
a given period. Thus, in particular, the annual crude death rate. (C.D.R.) denoted
by m for any given region or community is given by
$$m= \frac{annual. death. rate}{annual .mean. population} \times k$$
k=1000
The
crude death rate for any period gives the rate at which .the population is
depleted through deaths over the course of the period.
Merits
1. It is simple to understand and calculate.
2.
C.D.R. is “perhaps the most widely used of any vital statistics rates. As an
index of mortality, it is used in numerous demographic and public health
problems.
3.
Since the entire population of the region is exposed to the 'risk of mortality.
C.D.R. is a probability rate giving the probability that a person belonging to
the given population will die in the
given period.
Demerits. Most serious drawback of crude death rate is that it completely
ignores the age and sex distribution of the population. Experience shows that
mortality is different in different segments of the population. Children, in
the early ages of their life, and the older generation are exposed to higher
risk of mortality as compared to younger people. Moreover, mortality rate is
also different for females, irrespective of age groups, than their male
counterparts. C.D.R. is not suitable for comparing the mortality in two places
or same place in two periods unless
Remark. We can compute the crude death rate for males and females separately.
For example, crude death rate for males in the given region during the given
period is given by the formula
$$\text{C.D.R. for males} = \frac{^mD}{^mP} \times 1000 = \frac{\sum_{x} ^mD_x}{\sum_{x} ^mP_x} \times 1000$$
Where mD is the number of male deaths and "' mP
is the male population in the given region during the given period. Similarly
Female deaths Female population is
$$\text{C.D.R. for females} = \frac{\text{Female deaths}}{\text{Female population}} \times 1000 $$
$$= \frac{^fD}{^fP} \times 1000 = \frac{\sum_{x} ^fD_x}{\sum_{x} ^fP_x} \times 1000$$
C.D.R. is generally less than male C.D.R.
Specific Death Rates (S.D.R.). In order to arrive at a more useful figure
than C.D.R. we must take into account the fact that the mortality pattern is
different in different segments of the population. Various segments may be age,
sex, occupation, social status, etc. For example, the people engaged in infant
or child welfare work would be interested to know the mortality condition in
the age groups below 1 year, 1-4 years, 5-9 years, etc. : those engaged in
maternal health programmes would like to know the number of deaths occurring
among women in the reproductive period (usually 15 to 49 years) : insurance
authorities would be interested in the mortality pattern at different ages of
the Population.
Death rate
computed for a particular specified section of the population is termed as
specific death rate (S.D.R.). S.D.R. for a given geographical region during a
given period
$$\text{S.D.R.} = \frac{\text{Total number of deaths in the Specified}\\ \text{ Section of the population in the given period}}{\text{Total population of the Specified Section in the same period}} \times $$
k =
1000 usually. Usually S.D.R. is computed specific to (i) age. and (ii) sex.
Age-Specific Death Rate (Age S.D.R.).To formulate ideas mathematically,
$$ \\
^mD_x = \text{Number of deaths in the age-group (x, x+n)}$$
i.e., number of deaths among the persons with age x or more but less than x+n, in a given region during a given period, t (say).
$$ \\ ^nP_x = \text{Total population of the age-group x to (x+n)}$$
Then the age-specific death rate for the age-group x to x+n, usually denoted by
$$\ ^nm_x, \text{is given by} \\$$
$$^nm_x = \frac{^nD_x}{^nP_x} \times 1000, \quad \text{where} \, m = 1,2,3, \ldots \\
\text{Age-specific death rate for male} \\
^m_nm_x = \frac{^m_nD_x}{^m_nP_x} \times 1000 \\
\text{Age-specific death rate for females} \\
^f_nm_x = \frac{^f_nD_x}{^f_nP_x} \times 1000,$$
Merits. The death rates specific to age and sex overcome the drawback of
C.D.R., since they are computed by taking into consideration the age and sex
composition of the population. By eliminating the variation in the death rates
due to age-sex distribution of the population S.D.R’s provide more appropriate measures of the relative mortality situation
in the regions.
Demcrits 1. However, S.D.R.’s are not of much
utility for overall comparison of mortality conditions prevailing in two different
regions,
say. A
and B. For example, it might happen that for certain age-groups the mortality
pattern for region A is greater than that for B but for the others the case may
be opposite. Hence it will not be possible to draw general conclusion regarding
the overall mortality pattern in region A as compared to the region B. In order
to draw some valid conclusions, the different age and sex specific death rates must be combined_
to give a single figure, reflecting the
true picture of mortality in the region.
2.
Moreover, in addition to age and sex distribution of the population social,
occupational and topographical factors come into operation causing what is
called diferential mortality. S.D.R.’s completely ignore these factors. In
order to eliminate such spurious effects, standardised death rates are compute
Standardised Death Rates the crude death rates in terms of age-specific
death rates for two regions A and B are given respectively by
$$^a_m = \frac{D_a}{P_a} \times 1000 =\frac{\sum_{x} ^am_x^ap_x}{\sum_{x} ^ap_x}$$
$$^b_m = \frac{D_b}{P_b} \times 1000 =\frac{\sum_{x} ^bm_x^bp_x}{\sum_{x} ^bp_x}$$
The expressions in above are nothing but the
weighted arithmetic means of the age-S.D.R., the weights being the
corresponding populations in the age-group.
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