ABSTRACT
In the discussion of the normal frequency distribution mention has been made several times of the percentage of occurrences within certain limits, or of the chance of certain values occurring. This introduces a theme which is fundamental to the whole of statistical analysis, namely the theme of probability. In the case of a large proportion of analyses one of the main purposes is to assess the probability that given values are likely to occur, or to be exceeded, or not to be reached. From other points of view the problem may also be posed in a rather different way although it is still basically the same problem. Thus the question may be asked as to the probability that certain events are likely to occur at given intervals, or that a certain distribution pattern has some significant meaning. Moreover, even to interpret the average properly it is necessary to think in terms of probability–the probability of its being exceeded or not, for example.
