The sources of business cycle fluctuations are mainly supply shocks like technology, oil prices, and labor supply for long-term changes in output. Demand shocks affect output in the short-term. Aggregate demand shocks contribute to 20-30% of output fluctuations, while technological shocks account for 25% of cyclical changes and 33% of long-term output variance. Oil price shocks were significant in the 1970s and 1980s. Shocks affecting labor input explain the rest of output fluctuations, about half of its variance at all frequencies.