One shortcoming in the literature on policy framing has been the absence of analytic models through which to explicate change. This paper advances research in this area in three related ways. First, it links policy frames to the actors who employ them. Second, based upon this linkage it proposes two complementary approaches for examining longitudinal change in policy framing: an actor representation approach and a frame adoption approach. Third, it assesses the relative contribution of each process using demographic decomposition analysis. This analytic framework is illustrated using the case of debates over welfare reform in the United States during the 1960s and 1970s. The findings are consistent with expectations from the frame adoption approach, suggesting that ideational diffusion was largely responsible for changing discourse during this period. (Contains 4 tables, 2 figures, and 7 notes.)