re: #198 Bert’s House of Beef and Obdicuts

Those variables are consistent across contraception types, though, so I’m failing to see the relevance of them being many.

Because for the most part they work against conception. First, it’s only 40% of this small sample that are positive, so the numbers in the population as a whole might be smaller. Second, the ones that were positive were not very positive, i.e. the numbers were very low, even when present. Third, not all the positives contained healthy, motile sperm. Fourth, the volume of preejaculate is generally less than ejaculate. The study points out that the number of sperm found even in the samples with the highest sperm count would be considered barely fertile if that were for ejaculate, and associated with less than a 2.5% chance of pregnancy within a year of trying.

Although our pre-ejaculatory samples often contained sperm with equivalent concentration and motility to what would be regarded as fertile in ejaculatory samples, the actual number of sperm in the pre-ejaculates was very low. We are unable to say how this finding might translate into the chances of pregnancy if these samples of pre-ejaculate were deposited in the vagina except that the chances would not be zero. All but one of our pre-ejaculatory samples contained fewer than 23 million sperm, and values as low as this were seen in ejaculatory samples of less than 2.5% of men whose partners conceived in less than 1 year

So, you have a fraction of a fraction of the population, producing small volumes of fluid with very low numbers of sperm.

Okay, then consider what percentage of the population practices coitus interruptus as their sole contraception - a small percentage. Consider what percentage of those do it consistently correct. Consider what percentage of those are having intercourse on a regular basis.

You’re looking at fractions of fractions of fractions of fractions, and all with low probability.