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* To whom correspondence should be addressed. E-mail: rpalra62{at}comcast.net.
We retrospectively mined and modeled data to answer to 3 questions. 1) Relative to an estimate based on ~20 semen samples, how imprecise is an estimate of an individual's total sperm per ejaculate (TSperm) based on 1 sample? 2) What is the impact of abstinence interval on TSperm and TSperm/hour? 3) How many samples are needed to provide a meaningful estimate of an individual's mean TSperm or TSperm/hour? Data were for 18-20 consecutive masturbation samples from each of 48 semen donors. Modeling exploited the gamma distribution of values for TSperm and a unique approach to project to future samples. Answer-1. Within-individual coefficients of variation were similar for TSperm or TSperm/hour abstinence and ranged from 17 to 51%; average ~34%. TSperm or TSperm/hour in any individual sample from a given donor was between -20% and +20% of the mean value in 48% of 18-20 samples per individual. Answer-2. For ~80% of individuals, TSperm increased in a nearly linear manner through ~72 hours abstinence. TSperm and TSperm/hour after 18-36 hours abstinence are high. To obtain meaningful values for diagnostic purposes and maximize distinction of individuals with relatively low or high sperm production, the requested abstinence should be 42-54 hours with an upper limit of 64 hours. For individuals producing few sperm, 
7 days abstinence might be appropriate to obtain sperm for insemination. Answer-3. At least 3 samples from a hypothetical future subject are recommended for most applications. Assuming 60 hours abstinence, 80% confidence limits (CLs) for TSperm/hour for 1, 3 or 6 samples would be 70-163, 80-130, or 85-120% of the mean for observed values. In only ~50% of cases would TSperm/hour for a single sample be within -16 and +30% of the true mean value for that subject. Conclusions. Pooling values for TSperm in samples obtained after 18-36 or 72-168 hours abstinence with values for TSperm obtained after 42-64 hours is inappropriate. Reliance on TSperm for a single sample per subject is unwise.
Key words: Semen •
Semen Analysis •
Sperm •
Spermatogenesis •
abstinence interval •
imprecision of total sperm •
meaningful semen data
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