The Arbeitskreis Markt- und Sozialforschungsinstitute (ADM) allows infas to draw random samples on the basis of a current selection framework.
infas is not only a member of the industry association ADM, but also active in the working group random samples there and has access to the most up-to-date selection framework. As a result, infas is one of the few social research institutes that can make use of the well-known selection frameworks of ADM that are often required in tenders. This includes several networks for face-to-face interviews via the random route approach. In addition, the population selections for landline and mobile phone sampling are provided with an annual update.
Investigations, partly with infas participation, confirm that in the meantime around every second connection is no longer listed in generally accessible registers. The highest share of unlisted fixed network connections in major cities. In addition, younger people, single households, and low-educated people are more likely to be out of the phone book than older or multi-person households.
In addition to listed numbers (entered in telephone registries), we therefore use randomly generated numbers in the sampling and collect them with appropriate inclusion probabilities. In Germany, a solution has been developed by Häder / Gabler in this context, which has been tested in practice on a large scale.
Both the selection frame for landline numbers, as well as the selection frame for mobile numbers is based on the Häder / Gabler method. With this method, telephone numbers are generated synthetically in the fixed net or in the portable radio, since generally accessible directories such as telephone books offer also in the fixed net range only an incomplete selection frame.