enough to find statistically significant monotonic relationships between all contiguous pairs of strata. Three measures of screening scale performance were then calculated for each stratum: positive predictive value (PPV; the proportion of the respondents in the stratum who made an attempt), sensitivity (SENS; the proportion of all attempters who were in the stratum), and specificity (SPEC; the proportion of all non-attempters who were in the stratum). We also calculated area under the receiver operator characteristic curve (AUC),47 a summary measure of prediction accuracy that, unlike the more familiar Cohen’s κ,48 is not influenced by marginal distributions.49
