I think you're just trying to justify an unjustifiable test to protect your ego.
First, if you're just hiring assistants from the Philippines they could just have someone else take the test or get around it some other way.
Second, you have no good data to support this hiring practice. You're free to use it, but it's no better than just hiring a random person from your pool of applicants. You might as well screen based on their favorite color too to just make up filtering criteria.