Every once in a while I reread something that I've reported across editions of my texts, scratch my head, and ask myself: Is this really true?
Such was the case as I reread my reporting that “With the help of 382 female and 312 male volunteers. . . Masters and Johnson monitored or filmed more than 10,000 ‘sexual cycles.’”
I wasn't just makin’ stuff up. Masters and Johnson do report (on page 15 of Human Sexual Response) their “conservative estimate of 10,000 complete sexual response cycles” in their laboratory (some involving multiple female orgasms).
But let’s do the numbers. If they observed 10,000 complete sexual cycles over eight years (from 1957 to 1965), then they averaged 1,250 sexual cycles observed per year. Could we assume about an hour dedicated to each observation—including welcoming the participant(s), explaining the day’s tasks, attaching instruments, observing their behavior, debriefing them, and recording their observations? And could we assume about 40 weeks a year of observation? (Meanwhile, they were also running a sexual therapy clinic, writing, managing a lab, etc.)
So . . . doing the numbers . . . that’s roughly 31 weekly hours observing sex . . . for eight years.
It boggles the mind. And one wonders: Wasn't there some point of diminishing returns from observing yet another 1000 hours of sex . . . assuming Masters and Johnson reported truthfully?
I have no basis for doubting the accuracy and integrity of Masters and Johnson’s reporting. But I do, in a spirit of curiosity, scratch my head.
 In Human Sexual Response, they report gathering data over “eleven years” (pp. 9, 20). But Johnson didn't join Masters until 1957, and Johnson biographer Genoa Ferguson reports that Johnson “began doing sexual function research 6 months into her research position.” Also, Masters and Johnson report (p. 10) that the first 20 months of the observations—presumably by Masters without Johnson—involved medical histories of 118 prostitutes, eleven of whom “were selected for anatomic and physiologic study.” Ergo, although Masters and Johnson’s reporting leaves the exact study period ambiguous, it appears that the great majority, if not all, of the reported 10,000+ “complete sexual responses cycles” were observed during the seven or eight years after Johnson began her work with Masters. They also do not document the lab layout, or precisely how they observed their subjects. (As a point of contrast, Stanley Milgram’s similarly classic Obedience to Authority did precisely report on the participants, methods, and results of his various experiments, including drawings of the lab layout and equipment.)