1957 - United Nations Statistics Division

2 Substantially accurate statistics of births and deaths;
doubtful or deficient data on migratory movements,
or no account taken of such movements.
3 Birth and death statistics of undetermined reliability
(adequacy of migration data is disregarded).
4 Birth and death statistics which are stated to be deficient
(adequacy of migration data is disregarded).
5 Mathematical extrapolation (or interpolation), at
least three censuses having been taken since 1900.
6 Mathematical extrapolation (or interpolation), less
than three censuses having been taken since 1900.
7 Assumed rates of increase not derived by mathematical
extrapolation.
S None, base figure being held constant.
Method of adjustment not ascertained.
Alphabetic part: The arrangement of letters and numerals
in the classification scheme follows, in general,
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
file 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. The accuracy of estimates
obtained directly from such registers is relatively
independent of the periodicity or recency of population
censuses or of the reliability of birth and death statistics.
Therefore, generally speaking, continuous registers lead
to estimates which are superior to those derived from
censuses.
Estimates based on census enumerations are coded "A",
"B", or "C", according to the date of the last census, as
indicated above. No qualitative distinction among censuses
has been attempted, but it should be understood
that not all censuses are of comparable accuracy.
Estimates based on non-censal counts or partial censuses
are coded "n". 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 African 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 "nO"), 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 are coded "E".
Such estimates should be regarded merely as rough indications
of probable population size.
Numerical part: The numerical part of the code distinguishes
three types of time adjustment. The first type,
that is, adjustment on the basis of statistics of births,
deaths, and migration, is coded "I" if the data are held by
official and other reliable sources to be substantially accurate,
"2" if the components of natural increase 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 reliabiI-
17
ity, 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 is, on the
whole, an inferior method as compared with the first
type, except in cases where vital statistics or migration
data are deficient. The type of curve selected and the
length of the intercensal or postcensal interval also have
some bearing on the accuracy of the estimates obtained
by this method. Since the availability of more than two
census counts gives more information on past trends in
popUlation growth and more latitude in the choice of
curves, a distinction is made between countries having
had at least three censuses since 1900 (coded "5") and
those having had less than three (coded "6").
The third type of adjustment, an assumed rate of increase
not derived by mathematical interpolation or
extrapolation, is coded "7". Estimates obtained in this
way may contain large errors, 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 base data nor available information on population
change permit the use of a more reliable method.
An estimate held constant at the value for the base date
is usually of the lowest order of reliability and is coded
"S". It often represents lack of information both as to
popUlation size and as to rates of change. 5
Reliability of code: Even though it is possible to grade
roughly the two components of the code, 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 favourable
position with respect to one part of the code and a less
favourable 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
"0", "I" 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.
Applicability of code: Although the code appears in
Table I only, it refers to the estimates for 1956 wherever
they appear. For countries with a regular history of censustaking,
it is probably safe to assume that the method
given applies also throughout the post-war series 1947­
1955. But for the many areas in which the first census in
many years was taken recently, the code is applicable only
to the post-censal estimates and, even for these, it decreases
in applicability as the post-censal period is
lengthened.
Age and sex reporting
Statistics classified by age and sex are presented in 14
tables of this Yearbook. Table 4 presents enumerated and
5 For a more detailed discussion of the elements of the code, see
Methods of Estimating Total Population for Current Dates, Manual 1
of Manuals on methods of estimating population. United Nations. Department
of Social Affairs. Population Division, document STjSOAj
Series A, Population Studies No. 10, New York 1952. 45 p.