From 1982–96 as an emergency physician, mainly in rural and small city settings in Montana, Byock maintained an interest in end-of-life care. In particular, he was interested in exploring, measuring, and developing therapeutic supports for the entirety of a person's experience of suffering, dying, and in well-being. Along with Melanie Merriman, Byock developed the Missoula-VITAS Quality of Life Index, a clinical assessment tool designed to measure subjective quality of life in persons with serious illness. The index was intended to fill a gap in clinical assessment tools, which at the time were mostly focused on physiological indicators or observable function, rather than on subjective evaluations of well-being and suffering. An insight derived from the tool's use is that subjective well-being may exist even in the presence of severe functional impairment and high symptom burden.