Score contribution per author:
α: calibrated so average coauthorship-adjusted count equals average raw count
Testing the number of components in finite normal mixture models is a long-standing challenge because of its nonregularity. This article studies likelihood-based testing of the number of components in normal mixture regression models with heteroscedastic components. We construct a likelihood-based test of the null hypothesis of <italic>m</italic><sub>0</sub> components against the alternative hypothesis of <italic>m</italic><sub>0</sub> + 1 components for any <italic>m</italic><sub>0</sub>. The null asymptotic distribution of the proposed modified EM test statistic is the maximum of <italic>m</italic><sub>0</sub> random variables that can be easily simulated. The simulations show that the proposed test has very good finite sample size and power properties. Supplementary materials for this article are available online.