The prevalence of medical services use. How comparable are the results of large-scale population surveys in Germany?

BACKGROUND The large-scale representative population surveys conducted by Germany's Robert Koch Institute (RKI) contain questions pertaining to health and its determinants as well as the prevalence and frequency of outpatient services utilization. The same holds for the Socioeconomic Panel (SOEP, Sozio-ökonomisches Panel) and the Bertelsmann Healthcare Monitor (Gesundheitsmonitor) surveys. The purpose of this study is to examine the comparability of the instruments used in these surveys and their results. METHODS The questions on outpatient care utilization examined in this study were taken from the public use files of the East-West Health Survey (Ost-West Survey; OW1991), the 1998 Federal National Health Survey (Bundesgesundheitssurvey; BGS1998), the 2003 Telephone Health Survey (TEL2003), and the 2009 German Health Update (Gesundheit in Deutschland aktuell GEDA2009). The study also used data from the 26 waves of the SOEP (1984-2009) and the 16 waves of the Bertelsmann Healthcare Monitor (2001-2009) studies. RESULTS In the OW1991 and the BGS1998, questions on outpatient services utilization differ by the types of physicians inquired about. The four-week prevalence of contact with general practitioneers (GP) was 29% in the OW1991; the twelve-month prevalence in the BGS1998 was 69%. The OW1991 and the BGS1998 also surveyed participants on the number of physician contacts made during those reference periods (average number of contacts: 1.8 over the previous four weeks (OW1991) and 4.9 over the previous 12 months (BGS1998)). The TEL2003 inquires into the three-month prevalence of contact with private practice physicians in general (63%) as well as the number of contacts with primary care physicians over the previous twelve months (88% with at least one contact, average number of contacts: 4.6, range: 1-92). In the GEDA2009 survey, 88% of participants reported having contacted a physician at least once over the previous twelve months and an average of 6.1 contacts with all physicians working under contract with the German statutory health insurance (SHI) funds. The 2009 SOEP survey revealed a 28% three-month prevalence of contact with all types of physicians and an average of 3.6 contacts (among participants who had made at least one contact during this period). According to the Bertelsmann Health Monitor, the twelve-month prevalence of contact with GPs was 82%, with the average number of contacts being 5.0. The Bertelsmann Health Monitor also surveys participants on contacts made with four other types of physicians; the OW1991 and the BGS1998 ask about contacts made with over ten different types of physicians when examining the frequency of services use. CONCLUSIONS Not only do the target groups of the RKI surveys, the SOEP and the Bertelsmann Health Monitor differ; their questions on outpatient care utilization also differ in terms of examined reference period and types of physicians contacted by survey participants, question wording including clarifications (e.g., asking the participant to also consider contacts not made "in person" with physicians when answering a question), and response categories. Therefore, unlike the results of the surveys' questions on inpatient care, the results of questions on the use of outpatient care services are not easily comparable, even those regarding contact with primary care physicians and GPs. The results of secondary analyses of German SHI claims data could be used to confirm the external validity of the surveys' results.