sub stdev{
        my($data) = @_;
        if(@$data == 1){
                return 0;
        }
        my $average = &average($data);
        my $sqtotal = 0;
        foreach(@$data) {
                $sqtotal += ($average-$_) ** 2;
        }
        my $std = ($sqtotal / (@$data-1)) ** 0.5;
        return $std;
}