demographic yearbook annuaire demographique 1951

tions in the intermediate ages (notably between 25 and 50
years) are relatively low while those in the older and younger
ages are relatively high. This combination yields a relatively
high total rate.
The population of Israel, on the other hand, has experienced
heavy in-migration (affecting roughly the same ages)
and consequently yields a relatively low total rate. Israel's
comparatively high median age reflects the centre of gravity
of the age distribution of the immigrant population, which
consists largely of young adults, and does not imply a correspondingly
high proportion of old persons.
Differences in sex composition at the various ages also
have their effect on crude rates, but this effect, although
statistically significant, is much smaller than that of differences
in age composition.
The following general guides for the interpretation of
crude death rates may now be stated:
1. Crude death rates are precisely comparable only among
areas of closely similar age composition.
2. Differences between high rates and low rates represent
real differences but tend to understate differences in
age-specific mortality. High rates (in the neighborhood
of 20 per 1,000, or higher) may be taken as a sign of
both a high mortality and a young population, for
death itself is largely responsible for carving out the
form of an age distribution.
3. A population in fairly rapid transition from high mortality
to low mortality may still be a relatively young
population and have crude rates resembling those of
older populations considerably further advanced in the
reduction of mortality (see Japan 1947 and Ireland
1946).
4. Year-to-year changes in the crude rate of a given area
are not much affected by changes in age composition
but over a period of years differences are likely to
accumulate which affect the comparability of the series
as a whole, the effect increasing with the passage of
time.
Trends in crude rates. In the light of the foregoing analysis,
it is possible to examine recent trends in crude death rates
with the appropriate reservations well in mind. Although
a precise quantitative adjustment of the data cannot be
made, a more careful interpretation of the statistics is quite
feasible.
Since it is clear that small differences must be distrusted
for purposes of comparison, the countries for which data are
available have been classified into five groups, representing
TABLE C
Number of areas with average crude death rates at specified
levels: 1930-1932 and 1948-1950
Average crude
death rate
(per 1,000)
1930-1932
All classes. . . . . . . . . . . . . . . . . . . . .. 89
Under 10.0. . . . . . . . . . . . . . . . . . . . 9
10.0-14.9. . . . . . . . . . . . . . . . . . . . .. 30
15.0-19.9.................. 26
20.0-24.9. . . . . . . . . . . . . . . . . . . . .. 18
25.0 or over. . . . . . . . . . . . . . . . . . . . 6
Number of areas
1948-1950
115
44
51
9
9
2
rather broad ranges in the crude death rate. Table C gives a
comparison of the distribution of 89 areas for the period
1930-1932 with that of 115 areas for the period 1948-1950.
The basic data are the average crude death rates for the
periods indicated. Where it was not possible to obtain data
for each of the three years, two-year averages or rates for
one year only were used.
The results indicate a marked shift in the direction of
lower rates in the later period. The median rate (computed
from the grouped data) for 1930-1932 is 18.9; for 1948-1950
it is 13.7. These medians are only rough measures of central
tendency, for the units considered are geographic areas
(or countries), not persons, and they vary enormously in
population size.
For several reasons, these data cannot be taken as fully
representative of changes and conditions in the world as a
whole. First, the geographic coverage of the early data is
not the same as that of the later data. The later set includes
more areas, but the earlier set contains certain areas that
could not be included in the later one (e.g. Korea, Taiwan,
Burma).
Second, the areas for which data are available constitute a
biased sample of the world's population. They include a
disproportionate share of the countries where mortality conditions
may be expected to be better than average. In terms
of geographic distribution, the representation is very uneven.
The areas for which data relative to all or part of the period
1948-1950 are shown in table C are distributed as follows
among the major continental divisions:
Africa .
North America .
South America .
Asia .
Europe .
Oceania .
USSR .
Number of
areas
19
28
10
17
32
9
Estimated
population
(in thousands)
45094
212 655
56055
556865
334 111
11 192
Per cent of
continental
total
23
98
50
44
85
87
The Americas, Europe and Oceania are well represented
in the data, but the rest of the world is only partly covered.
The coverage for Africa is particularly fragmentary. Less
than one-fourth the population of this continent is represented
and virtually all of that fourth is drawn from the
population of European stock and from the Moslem population
of North Africa.
The third consideration which limits the representativeness
of the data is the reliability of the basic statistics.
Problems of reliability are discussed in some detail in
Chapter III and need not be reviewed here. It is sufficient
to say that for many of the areas, the death statistics are
seriously deficient. This gives the rates a downward bias
which may in some cases amount to 50 per cent or more.
Errors ofestimate in the population base may either enhance
or reduce the errors caused by the understatement of deaths,
but this factor is probably less important as a source of
inaccuracy in the rates.
In order to assess the magnitude of declines in the crude
rate at various levels, data of 44 areas for which the statistics
are judged to be reasonably complete were classified by the
level of the rate in 1930 and cross-classified by the percentage
decrease, 1930 to 1950. The results are given in
table D. In one case the base year is 1932 (data not being
11