The Place of Censuses
Censuses of population play an important part in the government of nations, particularly with regard to the spatial allocation of resources. The earliest modern censuses, from which results have been widely published, can be dated from around the start of the nineteenth century, with the first census of population in 1790 in the US and 1801 in England and Wales. Censuses represent one of a range of methods for counting population which also includes continuous administrative and registrationbased systems, particularly favored in Scandinavia, and indirect methods such as estimation from satellite remote sensing. A census is an attempt, typically decennial, to measure the location and characteristics of the entire population at a single point in time, in contrast to continuous approaches which rely on tracking population members, usually for administrative rather than statistical purposes. These approaches all contrast with sample survey methods which do not attempt to directly record the entire population. A successful census offers the single most powerful combination of population coverage, geographical and socioeconomic detail within a single integrated dataset, and can support a variety of data outputs, including, for example, microdata samples and interaction data which describe migration and commuting flows. The most traditional output has been aggregate responses for geographical areas, which form the basis for most census mapping.
Historically, there have been multiple motivations for conducting a census. An understanding of population resources may be required for purposes as diverse as raising an army, organizing political representation, levying taxation, or allocating welfare funding. The results of a census may be particularly politically sensitive when, for example, they demonstrate the relative strength of different population subgroups, such as the proportions and degree of mixing between Protestant and Catholic groups in Northern Ireland or the various ethnic groups in South Africa. Where there are conflicts within a population, subgroups may actively boycott census enumeration in protest about government policy, challenge the results of a census as not adequately representing their interests or lobby for the inclusion of specific questions or definitions. Some population subgroups such as unregistered migrants may actively seek to avoid detection by government, including a census. A longstanding criticism of censuses and their analysis is that they include only questions which are acceptable to the prevailing government and are therefore fundamentally limited in their ability to challenge established power relations in a society.
Modern censuses are generally conducted under specific statistical legislation and incorporate sophisticated data protection techniques in an attempt to provide respondents with privacy assurances. These include the random swapping of individuals between areas, rounding, or modification of small counts and suppression of results for areas with small populations. The extent to which the census technical and legislative framework provides effective protection to the individual, rather than simply contributing to surveillance by the state, is a strongly contested issue and varies between national contexts. Any data adjustment process will have an impact on census mapping. In general, statistical disclosure control procedures have the biggest impact on data at the neighborhood or village level, but are negligible at the scale of cities and regions.
Nevertheless, since the advent of computer based census operations the user base for census data has increased dramatically. Computer readable census outputs are widely used by central and local government, healthcare planners, academic researchers, and the commercial sector for demographic analysis and business or service planning. Census mapping, in the 1970s the preserve of university computer laboratories, is now readily undertaken online by schoolchildren. There is thus a strong tension between increasing the content and outputs of censuses to meet contemporary demands versus a desire to maintain comparability over time and preserve response rates. Internationally, census response rates are falling due to both public concerns over the privacy of personal information and increasing difficulty in accessing and delivering census forms to every household. In the early 2000s nations are adopting different strategies to provide the statistical information required by government – either through increasing reliance on administrative data sources or by spreading census enumeration over time. France has adopted a rolling census, aiming to cover all areas of the country during a 5 year time period, while the US has moved to a short form only census accompanied by a continuously administered sample survey. In addition to these alternative strategies, increasing effort is required in order to deal with the impacts of census nonresponse, including enumerator follow up of households from which there is no return and statistical imputation of missing values in the census data.