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APA Citation
Williams, D. I., Stephenson, J. M., Hart, G. J., Copas, A., Johnson, A. M., & Williams, I. G. (1996). a case control study of HIV seroconversion in gay men, 1988-1993: what are the current risk factors?. Sexually transmitted infections, 72(3), 193–196. http://access.bl.uk/ark:/81055/vdc_100181698235.0x000061