Short-term forecasts of real gross domestic product (GDP) are typically based on assumptions around the expenditure components of GDP, which are consumer spending, government spending, business investment, and foreign trade. Longer-term forecasts of GDP are based on the supply-side factors of production, which are capital, labor, and total factor productivity (TFP). The capital contribution to growth measures the growth in the supply of capital, be it buildings, machinery, or software. The labor contribution to growth measures the growth in the supply of workers (quantity) and the increase in skill levels (quality). Finally, TFP refers to the efficiency with which capital and labor inputs are used in the production process.