A total of about 40% of interviews in German market research is currently conducted over the telephone. Since the late 1990s a sampling frame, developed at ZUMA (Gabler-Häder design), has become increasingly popular in Germany which contains both directory-registered and unregistered telephone connections only available via local exchange. This sampling frame is updated biannually.
On behalf of research partners from the university-based social research GESIS will draw samples for nationwide as well as, if needed, regional surveys.
Moreover, in recent years a tendency has been manifested which possibly makes the singular future use of this sampling frame appear insufficient to cover the totality of private households: A growing share of households is solely to be reached via cellular telephones. Therefore, GESIS has developed a sampling frame for cellphone samples which is also available.
This enables a dual-frame approach for a survey using both a landline and a mobile phone sample. The results are combined by weighting.