Within-subject variability of human semen in regard to sperm count, volume, total number of spermatozoa and length of abstinence.

The within-subject variability of the semen sperm count (n), volume (v) and the total number of spermatozoa (N) was studied on 220 ejaculates from 36 normal subjects after an abstinence of 7 days or less. For each of the three variables, the within-subject standard deviation, sigma, was practically proportional to the mean, mu; the common value of the coefficient of variation sigma/mu for all subjects was very high: 0.39 for n, 0.28 for v and 0.55 for N. The 95% confidence intervals based on a single ejaculate were asymmetrical and very large, the lower and upper limits being respectively 0.5 x n and 2.3 x n; 0.7 x v and 1.8 x v; 0.4 x N and 2.9 x N. The three semen characteristics for a given subject were highly correlated with length of abstinence: for an increase in abstinence of 1 day there were mean increments of 13 x 10(6)/ml for n, 0.4 ml for v, and 87 x 10(6) for N.