Labor productivity is generally measured by output per worker or per unit of labor. Total factor productivity measures output per unit of all factors of production, not just labor. A "unit" is a weighted average of labor and capital (and any other factors of production, if there are more than two). The United States has the highest economy-wide labor productivity in the world, although Japan has higher labor productivity in some manufacturing industries. Differences in labor productivity are due to differences in capital-labor ratios and differences in total factor productivity. A higher capital-labor ratio or higher total factor productivity results in higher labor productivity. Differences in total factor productivity are due to differences in technology, education of the work force, competition, regulation, trade protection, and other political and institutional features that affect the efficiency with which inputs can be transformed into output.