for ($x=10; $x<1000000; $x=$x*10){
	$error_rate = $x;
	print "Error rate = 1 every $x, errors = ";
	for ($y=0;$y<5;$y++){
		errortest();
	}
	print "\n";
}

sub errortest {
	$errors = 0;
	for ($n=0;$n<1000000;$n++){
		$random = int (rand($error_rate));
		if ($random == 1){$errors++}
	}
	print $errors, " ";
}

Output: 

Error rate = 1 every 10, errors = 99778 100371 99586 99912 99778
Error rate = 1 every 100, errors = 10007 9962 9803 10063 10132
Error rate = 1 every 1000, errors = 1004 1019 1049 1011 945
Error rate = 1 every 10000, errors = 90 84 87 79 83
Error rate = 1 every 100000, errors = 0 0 0 0 0