ABSTRACT
The need for statistical tests arises when the data are less than perfectly reliable and are highly variable. As a possibly familar example, suppose that you had a bathroom scale that was unreliable. If you got on and off it a few times in succession, you might find that sometimes you were a pound above or a pound below the last reading. If you only got on it once, read the weight, changed your diet for a week, then got on the scale again and found that you had gained or lost a pound, you would not know whether the random variations in the scale's readings were responsible or whether you had actually changed in weight.
