A study published in the Lancet recently made headlines because it presented research from the Million Women Study in Britain suggesting that happiness does not affect mortality. These findings contradict a large body of research about happiness and health. In this op-ed, Ed Diener, Sarah D. Pressman, and Sonja Lyubomirsky argue that the research is far from definitive, and point out important methodological concerns about the Million Women Study that call this finding into question.