Guidance by Rainer Schnell: “Linking existing administrative data sets on the same units is used increasingly as a research strategy in many different fields. Depending on the academic field, this kind of operation has been given different names, but in application areas, this approach is mostly denoted as record linkage. Although linking data on organisations or economic entities is common, the most interesting applications of record linkage concern data on persons. Starting in medicine, this approach is now also being used in the social sciences and official statistics. Furthermore, the joint use of survey data with administrative data is now standard practice. For example, victimisation surveys are linked to police records, labour force surveys are linked to social security databases, and censuses are linked to surveys.
Merging different databases containing information on the same unit is technically trivial if all involved databases have a common identification number, such as a social security number or, as in the Scandinavian countries, a permanent personal identification number. Most of the modern identification numbers contain checksum mechanisms so that errors in these identifiers can be easily detected and corrected. Due to the many advantages of permanent personal identification numbers, similar systems have been introduced or discussed in some European countries outside Scandinavia.
In many jurisdictions, no permanent personal identification number is available for linkage. Examples are New Zealand, Australia, the UK, and Germany. Here, the linkage is most often based on alphanumeric identifiers such as surname, first name, address, and place of birth. In the literature, such identifiers are most often denoted as indirect or quasi-identifiers. Such identifiers are prone to error, for example, due to typographical errors, memory faults (previous addresses), different recordings of the same identifier (for example, swapping of substrings: reversal of first name and last name), deliberately false information (for example, year of birth) or changes of values over time (for example name changes due to marriages). Linking on exact matching information, therefore, yields only a non-randomly selected subset of records.
Furthermore, the quality of identifying information in databases containing only indirect identifiers is much lower than usually expected. Error rates in excess of 20% and more records containing incomplete or erroneous identifiers are encountered in practice….(More)”.