Problem drug use prevalence estimation revisited: heterogeneity in capture–recapture and the role of external evidence. Hayley E Jones, Nicky J Welton, AE Ades, Matthias Pierce, Wyn Davies, Barbara Coleman, Tim Millar & Matthew Hickman. This article was published in the March issue of Addiction [111(3), 438–447]. However, the online Appendix was not included at the time of issue publication. Appendix S1. Additional details regarding the statistical methodology, full data set, estimated interaction terms, and code to run the final model in the WinBUGS software.The Supporting Information has now been added at the end of the paper and now appears online at http://onlinelibrary.wiley.com/doi/10.1111/add.13222/epdf. We apologize for this error.