In contrast to economics, business strategy research began with the presumption of heterogeneity within industries and has only recently come to grips with the question of how differences in efficiency are sustained in the face of competition. Thus, the earliest case research informed by the 'strategy' concept focused on the different approaches to competition adopted by firms within the same industry. As the field matured, attention turned towards developing quantitative measures of this diversity and, more recently, to its explanation in economic terms.