Let’s say the criterion for fairness we will use is that if, in flipping the coin 10 times, we get heads (or heads turn up) less than 5% of the time, we’ll say the coin is rigged and call the police on Lew. This 5% criterion is one standard that is used by statisticians. If the probability of the event (be it the number of heads or the score on a test or the difference between the average scores for two groups) occurs in the extreme (and we’re saying the extreme is defined as less than 5% of all such occurrences), it’s an unlikely, or in this case an unfair, outcome.
