According to the U.S. Bureau of Labor Statistics (BLS), U.S. labor productivity has increased by nearly 40 percent since 2000. To obtain the data used to create labor productivity measures, the BLS surveys businesses about their output of goods and services and the average weekly hours of full-time employees. When constructing its labor productivity measure, the BLS excludes government employees, self-employed people, managers, and part-time and temporary employees. Recent estimates indicate that including these forms of labor might reduce the growth in U.S. labor productivity by as much as one-half.

Why might the output of government workers be difficult to gauge for purposes of measuring labor productivity?