The Flaws in Population Data

Brian Sturgess - October 2017

Accurate world population data is immensely important in assessing the impact of people on the sustainability of the planet’s resources. According to World Economics there were an estimated 7.467 billion humans living on the planet in 2017. The Chart below shows that this number is expected to climb to reach 11.2 billion by 2100. 

This mass of people is a consequence of the acceleration in the rate of growth of global population after 1820. Before 1800 the growth in world population growth rate was below 1% per annum.  As shown in the Chart this increased sharply over the following century and a half reaching a peak rate of 2.1% in 1862. This rate of growth has already slowed down since then and is estimated to have fallen to an annual rate of 0.1% by 2100, just above replacement. Studies suggest that there will be a stock of around 10-11 billion humans by the end of the century.

Source: Our World in Data

Total global population size, however, is only an estimate based on the aggregation of the demographic data of individual countries. Unfortunately, it is at the national level that uncertainty about population data is greatest. Knowledge of a territory’s population size, structure, distribution and growth rates is essential for many purposes: planning, housing, education, and the availability of food and water resources and sewage. But for many countries there are grave doubts about the accuracy of population estimates based on both surveys and censuses. 

Measuring the size of the population of Nigeria, for example, is problematic. In a census carried out in 2012, the country’s National Bureau of Statistics, measured the population at around 166.2 million people. Estimates of Nigeria’s population in 2016 currently range from over 178.5 million to the United Nation’s projection of 186 million. This contrasts with an estimated population size of 45.2 million on the independence of Nigeria in 1960. The uncertainty is reflected in estimates of the size of Nigeria’s biggest urban are – Lagos. The Nigerian Government and the Lagos State government disagree about the city’s size with the government estimating a figure of 21 million against 17.5 million by the city authorities.  In historical terms large discontinuities in Nigeria’s population estimates based on census data also occurred as a result of the transition from colonial rule to independence.  The 1952 census would have been downwardly biased because the data would be used for estimating tax receipts. The 1962 census would be upwardly biased since the results would provide a base for voting, federal development spending and the distribution of representational seats in the national assembly. But although the most populous country in Africa, Nigeria is not the only developing nation country with inaccurate population estimates. Morton Jerven has pointed out that “underestimation of the population in colonial censuses and overestimation in postcolonial censuses is a general problem in sub-Saharan Africa.” 

But even in the developed world there are problems in estimating population accurately using official data. The 2011 census figures for the United Kingdom revealed serious discrepancies in the population count in the borough of Westminster in the heart of London. Westminster has a fluid population with a turnover of around a third of households every year. Data on council tax payers and doctor registrations suggested that the Office for National Statistics had missed around 21,000 households which, if uncorrected would have led to a fall in central government funding and the provision of services. Poor reporting of population can have significant economic consequences.

Users of reported population statistics need to be aware of the very significant flaws which are common even in developed countries. In emerging economies these flaws can lead to very severe distortions with implications for planning decisions.