PHP static method slower than objet method

This is the PHP code...

class SomeClass
{
   static function doTest($var) {return $var;}
}

class SomeObj
{
   function doTest($var) {return $var;}

   static function doTest2($var) {return $var;}
}

//bench static call
$starttime = microtime(true);
for ($i = 0; $i< 100000; $i++)
   SomeClass::doTest($i);
echo "Static call time: " , (microtime(true)-$starttime) , " ms
";

//bench object method 
$starttime = microtime(true);
$obj = new SomeObj();
for ($i = 0; $i< 100000; $i++)
   $obj->doTest($i);
echo "Object method call time: " , (microtime(true)-$starttime) , " ms
";

//bench static call
$starttime = microtime(true);
for ($i = 0; $i< 100000; $i++)
   SomeObj::doTest2($i);
echo "Static call (when the static is in the same class of object method) time: " , (microtime(true)-$starttime) , " ms
";

...and these are the results (simply reload page to do another test):