Systematic reviews (SRs) are useful tools in synthesising the available evidence, but high numbers of overlapping SRs are also discussed in the context of research waste. Although it is often claimed that the number of SRs being published is increasing steadily, there are no precise data on that. We aimed to assess trends in the epidemiology and reporting of published SRs over the last 20 years. A retrospective observational study was conducted to identify potentially eligible SRs indexed in PubMed from 2000 to 2019. From all 572,871 records retrieved, we drew a simple random sample of 4,000. The PRISMA-P definition of SRs was applied to full texts and only SRs published in English were included. Characteristics were extracted by one reviewer, with a 20% sample verified by a second person. A total of 1,132 SRs published in 710 different journals were included. The estimated number of SRs indexed in 2000 was 1,432 (95% CI: 547-2,317), 5,013 (95% CI: 3,375-6,650) in 2010 and 29,073 (95% CI: 25,445-32,702) in 2019. Transparent reporting of key items increased over the years. About 7 out of 10 named their article a SR (2000-2004: 41.9% and 2015-2019: 74.4%). In 2000-2004, 32.3% of SRs were based in the UK (0% in China), in 2015-2019 24.0% were from China and 10.8% from the UK. Nearly all articles from China (94.9%) conducted a meta-analysis (overall: 58.9%). Cochrane reviews (n = 84; 7.4%) less often imposed language restrictions, but often did not report the number of records and full texts screened and did not name their article a SR (22.6% vs. 73.4%). We observed a more than 20-fold increase in the number of SRs indexed over the last 20 years. In 2019, this is equivalent to 80 SRs per day. Over time, SRs got more diverse in respect to journals, type of review, and country of corresponding authors. The high proportion of meta-analyses from China needs further investigation. Open Science Framework (https://osf.io/pxjrv/).

Ziel der Studie: Routinedaten der Krankenkassen sind eine wichtige Datenbasis für die Versorgungsforschung. Ziel der Studie war es zu ermitteln, welche Unterschiede in der Versicherten- und Morbiditätsstruktur zwischen den Krankenkassen existieren und ob Alter und Geschlecht diese Unterschiede erklären. Methodik: Wir verwendeten 10 repräsentative Surveys (durchgeführt zwischen 2004 und 2008) des Bertelsmann Gesundheitsmonitors und damit Daten zu 15 089 Personen zwischen 18–79 Jahren. Unsere unabhängige Variable war die Zugehörigkeit zu 8 verschiedenen Krankenkassen(arten). Wir untersuchten die Prävalenz von Bluthochdruck, Diabetes, atopischen Erkrankungen, koronarer Herzerkrankung und Herzinsuffizienz. Wir berechneten verschiedene logistische Regressionsmodelle und adjustierten zunächst nach Alter und Geschlecht, dann für weitere Komorbiditäten und gesundheitsbezogene Variablen. Ergebnisse: Am häufigsten waren die Teilnehmer in den Betriebskrankenkassen (BKK; 20,1%) bzw. Allgemeinen Ortskrankenkassen (AOK; 19,2%) versichert, auf die private Krankenversicherung (PKV) entfielen 15,3%. Bezüglich Alter, Geschlechterverteilung, Bildungsstruktur und Erkrankungshäufigkeit zeigten sich deutliche Unterschiede. Bluthochdruck gaben 17,1–29,6%, Diabetes 3,9–11,4%, atopische Erkrankungen 4,3–6,7%, koronare Herzerkrankung 3,4–6,7% und Herzinsuffizienz 2,6–5,7% der Versicherten der einzelnen Kassen an. Auch nach Adjustierung für Alter und Geschlecht zeigten sich in der AOK bei allen 5 untersuchten Erkrankungen im Vergleich zur PKV statistisch signifikant höhere Werte. Für die BARMER und die DAK traf dies bei jeweils 3 Krankheiten zu (insgesamt bei 17 von 35 Vergleichen). Auch nach Kontrolle für zahlreiche weitere Komorbiditäten und gesundheitsbezogene Variablen fanden sich noch bei 6 von 35 Vergleichen zur PKV signifikant erhöhte Werte. Schlussfolgerung: Zwischen den Krankenkassen existieren Unterschiede in der Versicherten- und Morbiditätsstruktur. Unterschiede in der Morbidität lassen sich nicht durch Alter und Geschlecht erklären. Sie verbleiben teils sogar nach Adjustierung für relevante gesundheitsbezogene Variablen. Weitere methodische Arbeiten sind unumgänglich, um kontextspezifisch Stärken und Schwächen von Routinedaten einschätzen zu können. Aim: Claims data of health insurance companies are an important database for health services research. We investigated if there are differences in baseline characteristics and prevalence of chronic diseases between members of several health insurance funds in Germany, and if so, whether adjusting for age and sex could explain these differences. Methods: 10 representative surveys (conducted between 2004 and 2008) of the ‘Bertelsmann Health-Care Monitor’ comprising 15 089 participants aged 18 to 79 years were analysed. Our main independent variable was membership in one of 8 health insurance funds. The prevalence of self-reported hypertension, diabetes, atopic diseases, coronary heart disease and heart failure was studied. We first estimated the crude prevalence of chronic diseases stratified by these funds. We further fitted logistic regression models and adjusted for age and sex as well as for further comorbidities and health related factors. Results: Most respondents were insured in the BKK (Betriebskrankenkassen; 20.1%), the AOK (Allgemeinen Ortskrankenkassen; 19.2%) and private health insurances (15.3%). Substantial differences were found according to age, sex, educational level and prevalences of chronic diseases. Stratified by health insurance funds, prevalences ranged between 17.1–29.6% for hypertension, between 3.9–11.4% for diabetes, between 4.3–6.7% for atopic diseases, between 3.4–6.7% for coronary heart disease and between 2.6–5.7% for heart failure. When adjusting for sex and age, estimates for all 5 diseases were significant higher in AOK members compared to privately insured persons (3 diseases within the BAMER and the DAK, accordingly). In total, this was the case for 17 out of 35 comparisons. Even after adjusting for further comorbidities and health related factors 6 out of 35 comparisons showed significant increased estimates compared to privately insured persons. Conclusion: We found considerable differences in the prevalence of chronic diseases between German health insurance funds that remained after controlling for age and sex, and even after adjustment for further health-related variables. Further methodological studies are urgently needed to assess strengths and weaknesses of German claim data.