demographic yearbook annuaire demographique 1951

The second part, represented by a numeral, indicates the
method utilized for adjusting the basic data for a current
date and, where the method is the "balancing equation"
• (i.e., adjustment by means of statistics of births, deaths and
migration), the general quality of the data used in the
adjustment. Where the basic data on population size are
supplied each year, as is generally the case with a continuous
population register, no adjustment of the basic data is
required, and the second part of the code is shown as "0".
The full code and its interpretation are given in the note at
the end of table 1.
The general arrangement of letters and numerals follows a
descending scale of reliability. The code "RO" indicates
that the estimates were obtained directly from a continuous
population register and that they may be regarded as of the
first order of reliability. For present purposes a continuous
population register is defined as a registration system which
maintains an individual record for each person in the population,
a record being added for each birth, a record being
removed for each death, and provision being made for the
transfer of records with changes of residence. In so far as a
figure for the total population can be obtained directly from
such records each year, the accuracy of estimates so obtained
is relatively independent of the periodicity or recency
of population censuses or of the compilation of birth and
death statistics from another source. Generally speaking,
continuous registers lead to estimates which are superior to
those derived from censuses, whereas other non-censal
counting methods lead to less reliable estimates.
Estimates based on census enumerations are coded "A",
"B", "c" or "D", according to date and frequency, as
specified in the note at the end of table 1. No qualitative
distinction among censuses has been attempted, but it
should be understood that not all censuses are ofcomparable
accuracy.
Estimates based on non-censal counting procedures are
coded "E", regardless of their recency or frequency. This
category covers a fairly wide range of types, including ration
registrations, tax lists, hut counts, partial enumerations and
group enumerations such as are made in a number of
Mrican areas where the household, tribe or village serves
as the unit for counting. The accuracy of these counts varies
considerably, but as a group they may be regarded as yielding
results inferior to those generally obtained by the census
method of individual enumeration. In the case of annual
counts (coded "EO") the yearly repetition of the operation
is likely to lead to improved accuracy.
Estimates based on conjectures or guesses as to population
size made at some time in the past (i.e., before 1948) are
coded "F". In some cases these "base estimates" are held
constant; in others an assumed rate of increase is applied.
Such estimates are of a highly dubious accuracy and should
be regarded merely as rough indications of probable population
size.
The numerical part of the code distinguishes three types
of adjustment procedure. The first type, adjustment on the
basis of statistics of births, deaths and migration, is coded
"1" if the data are held by official and other reliable sources
to be substantially accurate, "2" if the components of natural
increases are substantially adequate but the adjustment
for migration either is not made or is based on inadequate
information, "3" if the birth and death data are of unknown
reliability and "4" if they are known to be deficient. In the
case of "3" or "4" the quality of the migration data is
disregarded.
The second type, mathematical interpolation or extrapolation
of two or more population counts (coded "5"),
is, on the whole, an inferior method as compared with the
first type, except in cases where vital statistics or migration
data are deficient. Interpolations are likely to be more
reliable than extrapolations; interpolations for a short intercensal
period are more reliable than those for a long intercensal
period. In specific cases the type of curve selected
may have some bearing on the accuracy of the estimates
obtained, but an evaluation of these has not been attempted.
The third type of adjustment, an assumed rate of increase
not derived by mathematical interpolation or extrapolation,
is coded "6". Estimates obtained in this way are likely to
be highly inaccurate, especially if the process is continued
over a long period of time. However, this is a method that,
in general, is applied only in cases where neither the basic
data nor available information on population change permit
the use of a more reliable method.
The various combinations of letters and numerals do not
lend themselves to a precise gradation from the most reliable
to the least reliable. This is so not only because of the factors
mentioned in the preceding paragraphs, but also because a
given set of estimates may have a favorable position with
respect to one part of the code and a less favorable position
with respect to the other part. It is difficult, if not impossible,
to rank such cases on a reliability scale. However, it may
be stated with some certainty that combinations of "R",
"A", and "B" with "a", "1" and "2" indicate a relatively
high level of reliability, that combinations of letters and
numerals at the lower end of the scale indicate a low level of
reliability and that other combinations represent a rather
wide variation in levels of reliability. Combinations of high
letters and low numerals, or the reverse (low letters and high
numerals) are unlikely to occur.
The codes refer to the series of estimates for the years
1948, 1949 and 1950, but not necessarily to every estimate
in the series. Where a census figure is given instead of a
midyear estimate and where an unofficial figure is shown
the code does not apply. These cases can be identified in the
table itself by reference to the census column or by the
symbol "x" which indicates an unofficial figure. In other
cases the method of estimation is known for one or two years
but not for all three. These cases are not identified in the
table because of space considerati~ns.However, since countries
are generally consistent about the methods used in
successive years, it is probably safe to assume that the same
classification applies throughout. The code does not refer
to the estimates for 1937 shown in the table, though it is
quite likely that similar methods were used in the preparation
of these data.
Table lA presents estimates of world population by continental
divisions for midyear 1950 together with data on
the area in square kilometres and the number of persons per
square kilometre. The area totals were obtained by summing
figures for all the countries shown in table 1. The estimates
of population are based mainly on the statistics for 1950
presented in the same table but include allowances for those
countries and population groups for which 1950 estimates
are not yet available as well as other adjustments considered
necessary for arriving at the best possible estimates for continental
regions. Because of the uncertainty of knowledge
about the population of some areas the world figure must
be regarded as only a rough approximation. The estimates
for Mrica and Asia are subject to considerable error; those
for North and South America are somewhat more reliable;
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