Peter Norvig has some good illustrations of this in this article on recognizing bad experiment design. Scroll down until you get to the pictures of dots on a square; the really random ones look less random than the ones that aren’t actually random.
It is common for random distributions to appear clumpy.
Peter Norvig has some good illustrations of this in this article on recognizing bad experiment design. Scroll down until you get to the pictures of dots on a square; the really random ones look less random than the ones that aren’t actually random.