Lifetime prevalence of novel psychoactive substances use among adults in the USA: Sociodemographic, mental health and illicit drug use correlates. Evidence from a population-based survey 2007-2014.

For the multiple response NPS variable, the significance of the differences among the proportions of NPS categories was evaluated through the non-parametric Cochran’s Q test, which yielded highly significant differences in the proportions of the four NPS categories (Cochran's chi2(3) = 1133.129, p<0.01) [ 43 ].

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