"The National Institutes of Health convened a group of experts that year to address the question 'What is the scientific evidence on the effectiveness of latex male condom-use sic to prevent STD transmission during vaginal intercourse?'
Most of the relevant published studies, they found, didn't use the kind of experimental design you'd want to see โ i.e.,
prospective design, in which the
researcher compiles data by following the subjects' behavior
going forward, rather than gathering data after the fact."