When one takes a hearing test, one is asked to press a button when a sound is first heard or hold the button down, releasing it when the sound goes away.  This is done at varying frequencies to determine hearing loss.  Such a test requires attention and concentration on the part of the examinee to be as accurate as possible.  If one wanted to defeat the efficacy of the test then one might "think of something else" rather than paying full attention.  I suppose that the hearing test should be scrapped as unscientific as it requires active mental participation and cooperation on the part of the person being tested.

Vision tests require the examinee to report whether one degree of magnification is clearer than another until the optimal lens magnification is discovered. If the examinee fails to concentrate or decides to "think about something else" rather than follow the instructions given, he might walk of the examination wearing “coke bottle” lenses and tripping over his own feet.  Guess we should scrap that unscientific examination as well.
;) ;D