The primary statistical analysis concerned the primary research question in the study - to evaluate the effectiveness of 12 months of maintenance treatment with oral methadone and co-prescribed heroin, compared with that of standard maintenance treatment with oral methadone alone - and was conducted for the trial on injectable and inhalable heroin separately. The primary analysis plan was developed without knowledge of the results of the study, and was approved before first indications of effectiveness, in terms of percentage responders in the various study conditions, were revealed. The draft Statistical Analysis Plan was approved at the meeting of the CCBH on September 2, 1999, and the final plan was approved on September 30, 1999 (CCBH, 1999b). Some technical amendments were made to the Statistical Analysis Plan on November 2, 2001, i.e. before any analyses were conducted (CCBH, 2001).