What if you're generally clumsy and not well balanced? I would assume that would hamper the result of the test.
I thought about that too. I think that self-assessment can be problematic, because we (w/o doctors degree in neurology) are not able to account for all variables affecting the test outcome and thus might be interpreting things as worse (or better) than they actually are.
I tend to do well on these tests from time to time, but I am generally clumsy and uncoordinated so that affects my results=)