Change in abstinence duration from 1st attempt – Nosyk, B., Anglin, M. D., Brecht, M. L., Lima, V. D., & Hser, Y. I. (2013). Characterizing durations of heroin abstinence in the California Civil Addict Program: results from a 33-year observational cohort study. American journal of epidemiology, 177(7), 675-682.