disorder continuum (slope). Graphical aids and plots of both parameters were used. Finally, differential item functioning (DIF) was performed in the PARSCALE[22] to test whether the probabilities of responding in different categories of consumption differed by population for the same underlying level of the attribute (the latent trait measuring severity). Items were evaluated for DIF by contrasting the IRT difficulty or location (bi) and slope (ai) parameters between the groups. Finally, test response curve (TRC) were plotted using the expected raw scores by the severity of the alcohol use disorder continuum for each study site. If the TRCs for sites do not substantially differ it can conclude that the significant item-level DIFs (if found) cancel out when the total scale is used [6].
