Each year, Statistics Korea publishes population figures for North Korea in a booklet based on surveys conducted by international organizations like the UN and data released by the Education Center for Unification under the Unification Ministry.
Most of these statistics were compiled based on a census the North took in 2008 with the UN's help.
North Korea's only previous census was in 1993, which established that the population is 21.21 million. Although rumor has it that several millions of people starved to death during the famine of the 1990s, nobody knows how many exactly died.
The second census in 2008 was taken with funds provided by the UN Population Fund to obtain basic data for humanitarian aid to the North. The North accepted the offer, presumably because it wanted a good grasp of the reality to develop its own economy.
The census lasted for 15 days, from Oct. 1 to 15, 2008. The North's Central Statistics Bureau surveyed 5,587,767 households nationwide by mobilizing a total of 35,000 census takers through municipal and provincial statistics offices. The questionnaire consisted of 53 questions about income, furniture, electronic home appliances, toilets, heating system, and tap water and sewage facilities, as well as basic personal information such as age and gender.
Like in South Korea, the North Korean census takers visited homes to ask the questions face to face. Statistics Korea officials flew to China, where they taught North Korean officials census methodology and techniques, and the South gave the North as much as US$4 million for the census from the Inter-Korean Cooperation Fund.
According to the census, the North's population was 24,062,000, up 2.85 million from 1993. Average life expectancy was 69.3 years, and infant mortality was 19.3 per 1,000. But these data are quite different from UN estimates, which put life expectancy at 67.3 years and infant mortality at 48 per 1,000. The credibility of the North's census data has not been verified.