A METAANALYSIS OF 61 SPERM COUNT STUDIES REVISITED

Objective: To re-examine data on sperm counts over time from 61 studie s from around the world. Design: Parametric analyses and flexible nonl inear models of the relation between sperm counts and time. Main Outco me Measure(s): Mean sperm concentrations per milliliter and regression coefficients for possible trends of concentrations over time. Result( s): A significant decline was found only in U.S. studies. Conclusion(s ): Studies from specific sites have found declines in sperm counts, bu t a world-wide decline has not been demonstrated. Rigorous assessment of statistical models should be done before conclusions are drawn. Fle xible smoothing models are a useful addition to currently available an alytic methods. (C) 1997 by American Society for Reproductive Medicine .