Analysis of 44 million hospital records from QLD, NSW, SA and WA has found that more than 200,000 patients travelled interstate to receive treatment.  New South Wales patients were the most likely to hop across state boarders, into Queensland and South Australia.  The findings are helping improve national health service planning as well as proving the value of national data linkage programs and the benefits they offer to researchers. The researchers say that the research also has implications for the design of long term studies.  The research, supported by the Population Health Research Network, was published in the Medical Journal of Australia.