Three NPV values were calculated: unadjusted NPV and NPV adjusted for clustering of observations through logistic regression and generalized estimating equation (GEE). Standard diagnostic accuracy statistics were calculated for all available paired episodes ( n = 1134). Self-report of any methamphetamine use in the previous 7 days by the time-line follow-back method was the index test. Weekly oral fluid samples over 12 weeks to determine methamphetamine (and amphetamine) concentrations were used as the reference standard. Particpants were 139 people dependent on methamphetamine. Three Australian outpatient addiction services took part. This study was a secondary (subgroup) analysis from a randomized controlled pharmacotherapy trial. The study aim was to estimate the NPV of self-reported non-use of methamphetamine compared with an oral fluid reference standard. For the treating clinician, the key accuracy statistic is the negative predictive value (NPV). Self-report is commonly used for routine monitoring, but the accuracy of self-report is not established. Treatment of methamphetamine dependence requires monitoring of recent use or abstinence.
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