Economic growth in fast-graying Japan has been “surprisingly” strong if measured per working-age adult, despite a much poorer showing in terms of growth per capita, according to a recent study. Three economists, including Jesus Fernandez-Villaverde from the University of Pennsylvania, analyzed the gross domestic product of advanced economies per working-age adult aged 15 to 64, instead of growth per capita, which is becoming a “misleading indicator for growth theory” due to those economies’ aging population. “Japan appears as a surprisingly robust economy” when demographics are considered, acc…