$sql = "appropriate select for response_id_1"
	$sth = $dbh->prepare($sql) or die("Could not prepare!" . $dbh->errstr);
	$sql = "appropriate select for response_id_2"
	$stm = $dbh->prepare($sql) or die("Could not prepare!" . $dbh->errstr);
	$start_1 = new Benchmark;
	for $i (0 .. $iterations) {
		$sth->execute() or die("Could not execute 1!" . $dbh->errstr);
		while ($data = $sth->fetchrow_array()) {
			$union{$data} = undef;
		}
		$stm->execute() or die("Could not execute 2!" . $dbh->errstr);
		while ($data = $stm->fetchrow_array()) {
			$isect{$data} = undef if exists $union{$data};
		}
		@isect = keys %isect;
	}
	$end_1 = new Benchmark;
	$diff = timediff($end_1, $start_1);