The figure below from my 2008 JHPPL paper with Steve Pizer and Ann Hendricks (ungated summary here), illustrates the overlap between the veteran and Medicare populations. The numbers are from approximately 2003, so they’re a bit different today, but not wildly different.
The whole pie represents all elderly Medicare beneficiaries, of which there were about 35 million around 2003. Of those, 10 million, or almost 30%, were veterans. Of course, the vast majority of veterans of that age are men. Though less than half of elderly Medicare beneficiaries are men (women live longer), it’s a rough estimate that 50-60% of male, elderly Medicare beneficiaries are veterans. Few know this fact, but that doesn’t make it untrue.
As the figure shows, of the 10 million elderly Medicare beneficiaries about 3 million were enrolled in the Veterans Health Administration (VA). Those 3 million VA-Medicare duals represented about 50% of total VA enrollment in 2003. So, there is a large overlap between the VA and Medicare. This fact is relevant to studying the VA, but is not widely appreciated or always considered. It’s also relevant, to studying Medicare, particular the male Medicare population, but VA use is rarely, if ever, incorporated into such studies. (For a comparison of VA and Medicare costs that ignores this overlap, see Appendix B of this CBO pdf document. H/t to Ashish Jha.)