“…Following Rao's (1948) article likelihood estimation appears not to have been pursued further until Hasselblad (1966Hasselblad ( , 1969 addressed the problem, initially for a mixture of g univariate normal distributions with equal variances. The likelihood approach to the fitting of mixture models, in particular normal mixtures, has since been utilized by several authors, including Hosmer (1973aHosmer ( , 1973bHosmer ( , 1974Hosmer ( , 1978, O'neill (1978), and Ganesalingam and Mclachlan (1978, 1979, 1980. Butler (1986) noted that Jeffreys (1932) used essentially the Expectation-Maximization (EM) algorithm in iteratively computing the estimates of the means of two univariate normal population, which had known variances and which were mixed in known proportions.…”