How does determining the official numbers of inhabitants work?
In contrast to traditional population censuses, not all household are questioned by interviewers in a register-based census. In the end, all inhabitants will nevertheless have been counted. How does it work?
To determine the official numbers of inhabitants, first of all, the municipal population registers are used. Data for the reference date of 9 May 2011 are transmitted from those registers to the statistical offices, where they are counted. However, this alone is not sufficient to determine the official numbers of inhabitants because the population registers involve overcoverage and undercoverage (outdated entries and missing entries), which bias the results. These errors must, and can, be corrected statistically by means of the results of surveys.
This is done in various ways because the census test of 2011 showed that the population registers in large municipalities have a higher percentage of outdated and missing entries than those in small municipalities. Therefore it was decided for municipalities with 10,000 or more inhabitants to apply a different method than for municipalities with less than 10,000 inhabitants.
In (large) municipalities with 10,000 or more inhabitants, the official number of inhabitants is determined as follows:
The basis for determining the official number of inhabitants of municipalities is the data from the municipal population registers. To find out how many outdated and missing entries there are in the population register data, a household survey is conducted in Germany, covering about 10% of the population. If, for example, 9 people are found to live at an address where 10 people are registered, the person registered in addition represents an outdated entry and must not be counted as one of the official inhabitants. Instead, the outdated and missing entries identified in the household survey are then extrapolated to the entire municipality.
In (small) municipalities with less than 10,000 inhabitants, the official number of inhabitants is determined as follows:
In small municipalities, the register quality is better on average than in larger municipalities, that is, there are few outdated or missing entries in the population registers. To identify them in the household survey, a high percentage of people in these municipalities would have to be questioned, that is, a sample with a very high sampling fraction would have to be drawn. This is why other correction methods are applied here which produce similar results. Persons who are registered with their main residence in several municipalities, with at least one of them having less than 10,000 inhabitants, get a questionnaire containing questions on their main residence (check for multiple registration) in accordance with Section 15 of the 2011 Census Act. If, at an address in a municipality with less than 10,000 inhabitants, an unusual difference between the population register data and the data from the census of buildings and housing is discovered, the inhabitants at this address are specifically questioned again to clarify the situation (survey to clarify discrepancies) in accordance with Section 16 of the 2011 Census Act. The relevant results are taken into account in determining the official numbers of inhabitants for municipalities with less than 10,000 inhabitants.
These procedures are applied only for the population at normal housing addresses. To avoid possible social discrimination, and for procedural and methodological reasons, the official number of inhabitants of residential establishments and collective living quarters (“special facilities” such as establishments for disabled persons or the elderly) is determined through a complete enumeration. The results of these surveys, too, are included in the official numbers of inhabitants.
