level, as about 7.3 years for the U.S. hotel industry; and for the U.S. restaurant industry, as about 8 years. Industry cycles versus business cycles Cyclical dynamics at the level of individual industries may present rather different patterns from those of the general business cycles. For example, while the fluctuations of many industries correlate with those in the aggregate economy, there were also many industries that are not sensitive to business cycles — such as the pharmaceutical, educational service, insurance carriers and public service industries; some other industries such as the health service industry even enjoy higher growth during recessions. In fact, it was estimated that "in any one recession [during the 1980s and the 1990s] only 60% of all industrial sectors were actually in a downturn." The timing, duration and amplitude of industry cycles can vary widely. Durable goods industries in the US are approximately three times more cyclical than nondurable-goods industries. Identification and measurement of industry cycles Industry cycles have been identified using either the ‘classical cycle’ approach or the ‘growth cycle’ approach. The former approach uses time series in levels of economic activities to define cycles; and only absolute decline in the activities qualifies as a ‘downturn’. While this approach is consistent with the approach used by the National Bureau of Economic Research (NBER) to identify business cycles in the US, cycles at the industry level are usually concealed by strong industry trends which dominate industrial series. Therefore industry cycles are more commonly identified using the ‘growth cycle’ approach, by separating the cyclical component of a time series from the underlying trend. Combining the growth cycle approach and other econometric techniques such as the Hodrick-Prescott filter, the industry cycles in the global semiconductor, PCs and flat panel display industries in the past decades are identified. Industry cycles can be further measured using techniques such as the Fourier analysis. For example, three most powerful cycles of the global semiconductor shipment data in the frequency domain are identified, with an average period of 4 years, 2.29 years, and 1.03 years accordingly (reverting to the original time domain). Drivers of industry cycles Three main mechanisms are suggested to be responsible for industry cycles, namely industry cycles caused by business cycles; industry cycles caused by mismatch and delay between different market dynamics including investment, capacity, price and sales; and industry cycles caused by the dynamics of innovation. Many industries boom when