One problem in assessing the impact of management is that it is an amorphous and multifaceted category, including a variety of possible activities. This problem has been addressed by the work of economists like Nicholas Bloom and John Van Reenen, who have been leaders in creating a survey of management practices in 12,000 firms across 34 countries, spanning a decade and a half. They have systematised, and quantified to a considerable extent, the measurement of management practices and quality.