Countries normally publish literacy statistics based only on indirect information collected as part of a census. Some countries have reported data from 7-8 censuses over the last century so these countries' literacy trends can be easily detected. But most countries have reported data from only 1 to 3 censuses so their trends may not show well. Over 30 countries have never published any literacy data. It must be understood that official statistics published by international and national agencies are less accurate than they appear to be, despite best intentions, as they are not based on the same kind of data for all countries.
Different countries use different types of indirect literacy measures.
Countries use different criteria to decide whether people are literate. Not all countries report data every 10 years. These problems force international agency experts to estimate literacy levels for many countries, as they are not given complete and comparable data for 10 year intervals. Think about it. All rights reserved.