Because the shape of the relationship between time and alcohol effects was expected to differ as a function of BrAC limb (e.g., Holdstock & de Wit, 1998), a regression spline was included in each model. For each individual, the spline variable at time t is equal to pmax(0, time t – timepeakBrAC). During the ascending limb this variable is equal to 0; during the descending limb it is equal to the time elapsed since peak BrAC. This places a “knot” at the time of the individual’s peak BrAC, allowing the trajectory of the relationship between time and outcome variables to change at that time. For placebo participants, the spline was yoked to the average time when alcohol participants achieved maximum BrAC (t = 80 min).
