Sexual risk of HIV transmission is missed by traditional methods of data collection.

Brief acts of unprotected anal sex (i.e.'dipping') have not been systematically measured in AIDS research. Eleven per cent of HIV-positive men who reported that they had not engaged in any unprotected insertive anal intercourse with an HIV-negative or unknown status partner reported that they did engage in insertive 'dipping'. Men reported 'dipping' an average of 5.1 times, representing 773 acts of insertive intercourse that would have been missed by traditional methods of sexual data behavior.