[The significance of a large number of health insurance funds and fusions for health services research with statutory health insurance data in Germany - experiences of the lidA study].

Since 1970 the health insurance system in Germany has shrunk by more than 90% to 132 statutory health insurance funds (SHI) at present. For studies using data from different SHI, this development means a reduction of contacts and a higher workload when requesting data. The latter is due to the fact that fusions bind resources in the health insurance funds. In order to avoid selection in studies among the insured, all SHI must be contacted. Additionally, 15 controlling institutions on the state and national level have to agree as determined in § 75 of the German Social Code number 10. The lidA study - a German cohort study on work, age and health intends to link primary and secondary data from all SHI of those insured who have given their agreement for participation. Since the beginning of the study in 2009 the number of SHI has been reduced by 70. Of the 6 585 interviews in 2011 approximately half of the interviewees agreed in written form that their individual health insurance data can be linked. This portion of the insured is dispersed among 95 SHI. At this point, 11 contracts with SHI are realised (approximately 50% of the insured) and 8 data controlling authorities have been contacted. The problems involved in the fusion of SHI and its meaning for research are explained in this article. The fusion of SHI makes sense for the long term. It will lead to a reduction of contacts and contracts that researchers have to establish in order to analyse the data. Therefore, this article also discusses the alternative of creating a meta-data set of all the data from the different SHI combined.