The Stock-Watson Experimental Coincident, Leading and Recession Indexes were revised beginning with the release for September 1997 (first available in November 1997). The revision reflected three changes in the original model described in Stock and Watson (1989):
 

• Data -- The Public-Private Interest Rate Spread is now computed as the difference between the interest rates on 3-month commercial paper (financial) and 3-month U.S. Treasury bills. All other data series have been updated to reflect new benchmarking, etc.

• Parameter Estimates -- All of the parameters in the model were re-estimated using data over the 1959:2-1997:5 sample period.

• Trend Function in the XLI/XRI model -- A stochastic trend was added to the XLI/XRI model. The trend, modeled as a random walk, was added as a time-varying intercept in the equation relating the coincident index to lagged values of the leading indicators. This component affects the XLI and XRI, but does not affect the XCI.