<Dd> (II) we fail to reject H when some alternative hypothesis H or H is true . (There are various notations for the alternative). </Dd> <P> In all of the papers co-written by Neyman and Pearson the expression H always signifies "the hypothesis to be tested". </P> <P> In the same paper they call these two sources of error, errors of type I and errors of type II respectively . </P> <P> It is standard practice for statisticians to conduct tests in order to determine whether or not a "speculative hypothesis" concerning the observed phenomena of the world (or its inhabitants) can be supported . The results of such testing determine whether a particular set of results agrees reasonably (or does not agree) with the speculated hypothesis . </P>

Significance level type 1 and type 2 error