Egenvall et al. Acta Veterinaria Scandinavica 2011, 53(Suppl 1):S4 http://www.actavetscand.com/content/53/S1/S4 and identity number being taken directly from this data- base, which will enhance merging to a large degree. If the work is done in collaboration with several database owners, the very results presented to these data base owners may lead to increased quality of data over time and increased access to data. The research in itself may therefore be helpful for the database owners. Merging their data with other data can provide insights on a quantitative level not to be found in any other way. Another advantage is that research using secondary databases may bring stakeholders together- enhancing awareness about both possibilities and limitations. Conclusion In addition to all the data quality and validity issues inher- ent in the use of a single database, additional obstacles arise when combining information from several databases. Loss of individuals due to incorrect or mismatching identi- fying information can be considerable. If there are any possible biases affecting whether or not individuals can be properly linked, misinformation may result in addition to the reduction in power. Issues of confidentiality may be more difficult to address across multiple databases. For example, human identity information must be protected, but may be required to ensure valid merging of data. There is a great potential to better address complex issues of health and disease in companion animals and horses by integrating information across existing databases. The challenges outlined in this article should not preclude the ongoing pursuit of this approach. Acknowledgements This article has been published as part of Acta Veterinaria Scandinavica Volume 53 Supplement 1, 2011: Databases in veterinary medicine: validation, harmonisation and application. Proceedings of the 24th Symposium of the Nordic Committee for Veterinary Scientific Cooperation (NKVet). The full contents of the supplement are available online at http://www.actavetscand. com/supplements/53/S1. Author details 1The Department of Clinical Sciences, Faculty of Veterinary Medicine and Animal Science, Swedish University of Agricultural Sciences, SE-750 07 Uppsala, Sweden. 2Department of Companion Animal Clinical Sciences, Norwegian School of Veterinary Science, Oslo, Norway. 3The Department of Anatomy, Physiology and Biochemistry, Unit of Equine Studies, Swedish University of Agricultural Sciences, Box 7046, SE-750 07 Uppsala, Sweden. Competing interests The authors declare that they have no competing interests. Published: 20 June 2011 References 1. Sørensen HT, Sabroe S, Olsen J: A framework for evaluation of secondary data sources for epidemiological research. Int J Epidemiol 1996, 25:435-442. Page 5 of 6 2. 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