public static double calculateVarianceSampleResult(double variance, long count) {
      return variance / (count - 1);
    }
Compute the sample variance by extending GenericUDAFVarianceEvaluator and
overriding the terminate() method of the evaluator.
ql/src/java/org/apache/hadoop/hive/ql/udf/generic/GenericUDAFVarianceSample.java