--- 
+++ 
@@ -23,7 +23,7 @@
      * size {@code n}, the mean is {@code n * m / N}.
      */
     public double getNumericalMean() {
-        return (double) (getSampleSize() * getNumberOfSuccesses()) / (double) getPopulationSize();
+return (double) (getSampleSize() * (double) getNumberOfSuccesses()) / getPopulationSize();
     }
 
     /**