PHP's array_key_exists vs. isset

test.php

<?php

$array = array(
  'a' => 'A',
  'b' => 'B',
  'c' => 'C',
);

$st = microtime(TRUE);

for ($i = 0; $i != 100000; $i++) {
  if (array_key_exists('b', $array)) {
    usleep(1);
  }
}

print 'array_key_exists = ' . (microtime(TRUE) - $st) . PHP_EOL;

$st = microtime(TRUE);

for ($i = 0; $i != 100000; $i++) {
  if (isset($array['b'])) {
    usleep(1);
  }
}

print 'isset = ' . (microtime(TRUE) - $st) . PHP_EOL;

Results:

array_key_exists = 0.88500714302063
isset = 0.70769381523132