This study ascertains the validity of a two solution factor of age at onset in alcohol dependence. Particularly, the age at onset of alcohol dependence can be decomposed by admixture analysis into two normal distributions, with a cut-off at 22 years. Our finding is in line with previous researches, which suggest that the cut-off between early and late onset groups should range between 19 and 25 years (Buydens-Branchey et al., 1989; Hingson et al., 2006a). This is the first study to examine whether the age at onset distribution in alcohol dependence is a mixture of several normal distributions. This approach was previously used successfully in bipolar type I affective disorder, in schizophrenia (Schurhoff et al., 2004), as well as in obsessive compulsive disorder (Delorme et al., 2005) and suicide attempt (Slama et al., 2009). The size of the epidemiological sample studied herein is large, and even more important, the NESARC is a national representative sample using a well validated interview, whereas previous studies using admixture test to examine the distribution of age at onset relied on relatively small and clinical samples.
