public double stdErr(){
  if (num == 0) {
    return 0;
  }
  return std() / Math.sqrt(num);
}

public double stdErr ( ) { if ( num == 0 ) { return 0 ; } return std ( ) / Math . sqrt ( num ) ; }
calculate the standard error of the mean ( sem ) : the standard deviation of the sample - mean ' s estimate of a population mean .
