Diameter distributions of Douglas-fir can be described by the empirical three-parameter lognormal curve, in which the variate is y = log(y' + yo'). Following a description of both a graphic and a numerical solution for the origin or third parameter yo', the logarithm of the origin is shown to be a linear function of the logarithm of the initial mean dbh (y') in a series of 16 distributions. Given the predicted origins Yo', the means and standard deviations of y = log(y' + Yo') are simple functions of log y'. Agreement between the observed and the expected frequencies is tested by x 2 .
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Bliss et al. (1964) studied this question.