Various measures are employed in the analysis of mortality. It is, however, sufficient to describe the following three basic measures for a general understanding of the process of mortality: the crude death rate, the infant mortality rate, and the expectation of life at birth.

Crude Death Rate: The crude death rate is the most simple and the cost commonly used measure of mortality, which can be quickly calculated and, at the same time, easily understood.

It is a ratio of the total registered deaths of a specified year to the total mid-year population, multiplied by 1,000. It is computed as follows:

Where:

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D is the total number of deaths registered during a calendar year (January 1 to December 31);

P is the total population at the middle of the year (July 1); K is 1,000.

The crude death rate of 9.45 indicates that, in 1973 in Greater Bombay, 9.45 deaths occurred per 1,000 populations. The crude death rate thus expresses the frequency of deaths in an entire population as a single number.

An important use of the crude death rate is that it provides one of the bases for computing the rate of natural increase in population. In this respect, it may be compared with the crude birth rate. Both these rates are computed from the same base and for the same purpose.

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For instance, if in a population in a given year, the crude death rate is 16 per 1,000 population and the crude birth rate is 36 per 1,000 population in the same year, then the rate of natural increase is 36 – 16 = 20 per thousand population, or 2 per cent.

The crude death rate is the most widely available index of the level of mortality. A rough classification of various countries according to mortality levels may be undertaken on this basis. This index also gives us a general idea about the trend in mortality in a particular area over a period of time.

Though this summary measure is a very useful indicator of the level of mortality in any population, it is not a refined measure, as is evident from its very name, and suffers from several limitations. One of these limitations arises because of the inadequate coverage of death statistics though this is not inherent in its very nature.

The crude death rates of several countries suffer from this weakness and it is for this reason that it has to be mentioned. Another limitation of this measure is that it hides the experience of population groups whose mortality varies a great deal.

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On the whole, it gives a greater weight age to the mortality experience of large groups in the population. As the crude death rate does not take cognizance of the differences in the age-sex structures of different populations and as the impact of mortality is not uniform for all ages, the crude death rats of different population are not strictly comparable.

For instance, the crude death rate for England and Wales in 1961 was 11.8, while it was 11.3 for Mexico in 1960. Does this mean that the impact of mortality is the same in both the countries?

Some facts about the age structure of these two countries need to be known before any comparisons can be made. In 1961, England and Wales had a larger proportion of adults, that is, 77.1 per cent of the population was of age 15 and above.

The corresponding percentage for Mexico was 55.6 in 1960. As the mortality at the adult stage is higher, the crude death rate of England and Wales naturally has a tendency to be higher than that of Mexico.

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When, however, the crude death rate of England and Wales was standardised with respect to the age distribution in Mexico, it was found to be 4.8 per 1,000 population, a much lower death rate than-that of 11.3 in Mexico. (The standardised death rate for England and Wales was computed by applying the age distribution of Mexico to the death rates of England and Wales).

To overcome the inherent limitations of the crude death rate, age specific death rates are used. As sex differentials in mortality are also of important dimension, it is customary to compute age-sex specific death rates.

In fact each measure of mortality is usually computed separately for males and females. The other measure of mortality used for comparing the mortality experiences of various populations is the expectation of life at birth.