1. Research Economist, Office of Productivity and Technology, Bureau of Labor Statistics, 2 Massachusetts Ave. NE, Washington, DC 20212 (corresponding author).
2. Economist, Office of Productivity and Technology, Bureau of Labor Statistics, 2 Massachusetts Ave. NE, Washington, DC 20212.
3. Economist (retired), Office of Productivity and Technology, Bureau of Labor Statistics, 2 Massachusetts Ave. NE, Washington, DC 20212.