Patient flow diagram for the randomized controlled trial of methadone and fentanyl in patients undergoing complex spine surgery. The diagram represents both the original randomized controlled trial and the preplanned long-term follow-up study. The diagram identifies the number of patients completely lost to long-term follow-up, the number of patients who reported the weekly frequency of pain (the primary outcome) at each of the four long-term follow-up times (i.e., at 1 month, 3 months, 6 months, and 1 yr after the operation), and the number of patients from whom responses were obtained at both 1 month and 3 months as well as at all four follow-up times.