Rates of illiteracy are generally derived from
national population censuses or sample surveys.
UNESCO defines a literate person as
one who can "with understanding both read and write a short
simple statement on [her or] his everyday life", and an illiterate
person as one who cannot "with understanding both read and
write a short simple statement on [her or] his everyday life".
This definition of literacy is widely used in national population
censuses and surveys, but its interpretation and application may
vary to some extent among countries, depending on national, social
and cultural circumstances. Furthermore, this concept of literacy
includes persons who, although familiar with the basics of reading
and writing, might still be considered functionally illiterate.
Thus, a measure of functional illiteracy would also be useful,
but such statistics are collected in only a few countries.
Illiteracy rate refers in general to the proportion
of the population who are illiterate, expressed as a percentage
of the corresponding total population. Illiteracy rates are shown
separately for the age groups 15-24 and 25 or over. For young
people in developing regions, literacy may be a better measure
of education than enrolment since it usually reflects a minimal
level of successfully completed schooling. It should be noted
that data are lacking for a number of countries or areas in the
developed regions. This is due to the fact that a question on
literacy was not included in the population censuses, since illiteracy
has been reduced to minimal levels through several decades of
universal primary education.