Facebook API - 计算返回非一致值的朋友

trying to get amount of facebook firiends via facebook api (PHP)

• using this API call :

                  $friends=$facebook->api('/me?fields=friends');
                  $friends=$friends['friends']; 
                  $amount = count($friends);
                  //$amount = 477
  

• using this API call :

                  $params = array(
                                  'method' => 'fql.query',
                                  'query' => "SELECT friend_count FROM user WHERE uid =me()",
                  );
                  $amount = $facebook->api($params);
                  //$amount = 488
  

• Why is there a difference for both the calls ?

• What is more accurate ?

• Is there a way to overcome this issue ?

Thanks