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Etymology

In 1928, Jerzy Neyman (1894–1981) and Egon Pearson (1895–1980), both eminent statisticians, discussed the problems associated with "deciding whether or not a particular sample may be judged as likely to have been randomly drawn from a certain population": and, as Florence Nightingale David remarked, "it is necessary to remember the adjective 'random' should apply to the method of drawing the sample and not to the sample itself".

They identified "two sources of error", namely:

In 1930, they elaborated on these two sources of error, remarking that

in testing hypotheses two considerations must be kept in view, we must be able to reduce the chance of rejecting a true hypothesis to as low a value as desired; the test must be so devised that it will reject the hypothesis tested when it is likely to be false.

In 1933, they observed that these "problems are rarely presented in such a form that we can discriminate with certainty between the true and false hypothesis". They also noted that, in deciding whether to fail to reject, or reject a particular hypothesis amongst a "set of alternative hypotheses", H, H..., it was easy to make an error,

these errors will be of two kinds:

In all of the papers co-written by Neyman and Pearson the expression H always signifies "the hypothesis to be tested".

In the same paper they call these two sources of error, errors of type I and errors of type II respectively.