title: Variability of semen parameters with time in placebo treated men.
abstract: OBJECTIVE
  We describe the variability of semen parameters with time in normal men receiving placebo. We also report the impact of season and geographic region, among other variables, on these parameters.
  
  
  METHODS
  Data from the placebo arms of 5 randomized, controlled trials were pooled. All trials set minimum standards for semen parameters as an eligibility criterion for entry. Semen parameters examined include volume, density, motility, total count, total motile count and morphology. Mixed model repeated measure analysis was used for statistical analysis. Coefficients of variation for each semen parameter and the percent change from baseline were calculated.
  
  
  RESULTS
  The mean within-subject coefficient of variation for each semen parameter ranged from a low of 10% to a high of almost 50%. The contribution of season and region to variability was negligible. The reduction in variability with an increasing number of samples per time point had decreasing returns beyond 2 samples.
  
  
  CONCLUSIONS
  There was considerable variation in semen parameters with time in subjects who received placebo. Variation could not be attributed to season or region. We observed a general negative trend in semen parameters in this population selected for normal baseline semen parameters, which was likely due to the placebo response or to regression toward the mean.
authors.affiliation: Office of New Drugs, Center for Drug Evaluation and Research, Food and Drug Administration, Silver Spring, Maryland, USA. jonathan.jarow@fda.hhs.gov
authors.forename: Jonathan P
authors.initials: JP
authors.lastname: Jarow
authors.forename: Xin
authors.initials: X
authors.lastname: Fang
authors.forename: Tarek A
authors.initials: TA
authors.lastname: Hammad
mesh_terms: D000293:Adolescent; D000328:Adult; D006801:Humans; D008297:Male; D008875:Middle Aged; D015990:Placebo Effect; D012621:Seasons; D055101:Semen Analysis / Q000706:statistics & numerical data*; D013997:Time Factors; D055815:Young Adult