demographic yearbook annuaire demographique 1951

those for Europe and Oceania may be regarded as fairly
accurate.
Table 2 presents, for the 172 countries having had one or
more censuses since 1900, the dates of such enumerations,
the total population enumerated at each census and the
area of the country at the time of the census. As in table 1,
estimates for excluded groups or underenumeration are
noted in so far as they are known. Where the area and
population at successive censuses were regarded as sufficiently
comparable, the average annual percentage rate of
change computed by the compound interest formula,
PI = Po (1 + r)t, is shown. Unusually high rates of increase
or decrease are explained in footnotes wherever the explanation
could be determined. However, a number of extreme
rates remain without annotation. Some ofthese are no doubt
largely attributable to differences in completeness of enumeration.
The footnotes to this table have been expanded
to give a more precise account of the territorial changes
that occurred during the periods covered by the statistics.
Since territorial footnotes in the later tables are generally
given in briefer form, it is necessary to refer to table 2
(and, in some cases, to table 1) to obtain information as to
the size of the area and the approximate number of persons
affected by the changes.
Table 3 gives annual estimates of total population for 136
areas. Data are shown for the years 1932 to 1950 and, unless
otherwise indicated, refer to the middle of the specified
calendar year. In cases where official estimates were available
only for 31 December the arithmetic mean of two consecutive
end-of-year estimates was computed and is presented
in this table as the midyear estimate. In previous issues
of the Yearbook estimates for 1 July were distinguished from
means of end-year estimates by notations shown in the
table. This distinction is not made in the present table on
the assumption that the difference involved is negligible.
In a few cases, where official estimates are regularly prepared
for a date other than 1 July or 31 December, the
official figures are given in the table with a note indicating
the date to which they refer. In years for which the results
of a current enumeration were available the census figure
has sometimes been preferred to a midyear estimate, regardless
of the census date, if the two figures appeared not to be
in sufficient agreement. Census counts are shown in heavy
type.
In a number ofcases where preliminary results of censuses
taken in 1950 or 1951 are only recently available, intercensal
estimates have not yet been revised and brought into agreement
with the new population counts. For some of the
series, the need for revision is obvious and may be readily
identified by inspection of the data shown in the table. In
other cases, only minor fluctuations are implied by the
unrevised data. Probably the intercensal estimates will not
be revised until final resultil ofthe new censuses are available.
AGE AND SEX COMPOSITION
Statistics of the population classified by 5-year age groups
and sex are presented in table 4 for 40 areas. This table is a
supplement to the one presented in the last issue of the
Yearbook since only new data or data not before presented
are shown. The total number of areas for which statistics for
one or more years are shown in the two volumes taken
together is 109. Unless otherwise noted, the data relate to
age in completed years (or age at last birthday).
Certain irregularities appear in the age-sex data of many
countries. These include: (1) underenumeration of infants
and young children, (2) heaping at ages ending in 0 and 5,
(3) a preference for even ages over odd ages, (4) unexpectedly
large differences between the numbers of males and
females at certain ages and (5) unaccountably large differences
between the numbers in successive or adjacent age
groups. Some of these irregularities are obscured or eliminated
when the data are combined into 5-year age groups,
but the underenumeration of young children, the aberrations
in the sex ratio and some of the fluctuations in numbers
generally are still apparent.
Comparison between successive censuses of statistics for
identical age-sex cohorts as well as study of the age-sex
composition in each census indicates these and other inconsistencies,
some of which are characteristic of even the most
"modern" censuses. Examination of the data on age and sex
presented in this and earlier issues ofthe Yearbook has shown
that in some cases the statistics are particularly faulty in
these respects. However, since further study is needed in
order to make an accurate appraisal, the results so far
obtained have not been incorporated in this issue of the
Yearbook. It is hoped that a reliable evaluation of statistics
by age and sex can be presented in a future issue. Meanwhile,
the data must be approached with some caution,
particularly for those areas or population groups where the
level of literacy is low and where census methods are not
the most rigorous.
VITAL STATISTICS
Statistics relating to births, deaths, stillbirths, marriages
and divorces are presented in tables 5 to 26. These data,
being based on registration records, vary widely in coverage
and completeness. In some areas registration is not compulsory;
in others it is compulsory for only a part of the
population (e.g., "Europeans" in certain African territories).
Some countries have developed "registration areas" which
comprise only a part of the country, the remainder being
excluded for reasons ofinaccessibility or because ofeconomic
and cultural considerations that make regular registration
a practical impossibility. Whenever the area covered by
registration is less than the entire country it is noted in
the tables.
In so far as possible, the data presented in these tables
refer to events occurring during the specified year rather
than to events registered during the year. However, a considerable
number of countries tabulate their statistics by
date of registration, including delayed registrations in the
statistics for the year when they were reported rather than
in those for the year when the births, deaths, marriages or
divorces occurred. The lag is normally less than a month
in countries with efficient registration systems and the effect
on annual totals is negligible; but in some areas a lag of as
much as two years is not uncommon. Where numbers are
changing significantly from year to year or where there is
an appreciable variation in the time elapsed between occurrence
and registration, the results may be misleading as to
the number of vital events that actually occurred during the
specified year. This consideration is particularly important
in relation to statistics of births. Deaths and marriages are
ordinarily more promptly reported.
Countries for which the data are known to be on a dateof-occurrence
basis are:
America, North:
Alaska [U.S.]
Canada
Canal Zone [U.S.]
Dominican Republic
(births)
Panama (beginning 1943)
Puerto Rico [U.S.]
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