Within-subject variability and the importance of abstinence period for sperm count, semen volume and pre-freeze and post-thaw motility.

The within-subject variability of semen sperm count (n), volume (v), total number of spermatozoa (N) and pre-freeze (mo) and post-thaw (m1) motility was studied on 564 ejaculates from 98 normal subjects after an abstinence ranging from 1 to 5 days. After logarithmic transformation of n, v and N, the within-subject variances for each variable were found to be similar for all subjects; the within-subject centered distributions were nearly normal and 95% confidence intervals were calculated. These three variables appeared to increase linearly with the length of abstinence. For both mo and m1, the within-subject variances were also similar for all subjects and this without logarithmic transformation. Their respective within-subject centered distributions were normal; mo and m1 were not influenced by the length of abstinence during the period studied.