Studies that investigated the issue didn’t found 100% protection. I think it’s an interesting test for overconfidence.
HIV transmission rates for any particular sex act are pretty low, even without protection: low enough that the difference from adding a condom usually wouldn’t register at percentage granularity. You’d be better off asking for the transmission rate relative to the unprotected transmission rate, but that’s fairly obscure information; I recall it being considerably higher than I’d anticipated, but I don’t remember exact figures.
In any case, I don’t think this is down to systematic overconfidence so much as it’s a consequence of bad information floating around in the culture. I’ll bet if you asked a hundred people on the street what the chances of contracting HIV from unprotected sex with a carrier were, and then asked them what percentage of that risk they’d experience if they added a condom, they’d overestimate the former and underestimate the latter by very large margins: one or two orders of magnitude on the former wouldn’t surprise me.
HIV transmission rates for any particular sex act are pretty low, even without protection: low enough that the difference from adding a condom usually wouldn’t register at percentage granularity. You’d be better off asking for the transmission rate relative to the unprotected transmission rate, but that’s fairly obscure information; I recall it being considerably higher than I’d anticipated, but I don’t remember exact figures.
In any case, I don’t think this is down to systematic overconfidence so much as it’s a consequence of bad information floating around in the culture. I’ll bet if you asked a hundred people on the street what the chances of contracting HIV from unprotected sex with a carrier were, and then asked them what percentage of that risk they’d experience if they added a condom, they’d overestimate the former and underestimate the latter by very large margins: one or two orders of magnitude on the former wouldn’t surprise me.