The Uncertain Trend in U.S. GDP

28 Pages Posted: 3 Jun 1997

See all articles by Charles R. Nelson

Charles R. Nelson

Dept of Economics

Christian J. Murray

University of Houston - Department of Economics

Date Written: January 14, 1997


Several recent papers conclude that U.S. real GDP is trend stationary, implying that all shocks are transitory and the long run path is deterministic. These inferences fail to take into account two problems: the distortion of test size in finite samples due to data-based model selection and the fragility of unit root tests in the face of plausible departures from the maintained hypothesis of temporal homogeneity. Indeed, additive outliers that alter the level of output for only one period reliably trigger false rejections of the unit root hypothesis when it is true and signal the presence of permanent shifts in trend that did not occur. Trend stationarity is not supported by the more homogeneous post-war data and if imposed would imply business cycles of implausible duration and pattern--the economy was 8% below the trend line in 1994.

JEL Classification: C22, E32

Suggested Citation

Nelson, Charles R. and Murray, Christian J., The Uncertain Trend in U.S. GDP (January 14, 1997). Available at SSRN: or

Charles R. Nelson (Contact Author)

Dept of Economics ( email )

Box 353330
Seattle, WA 98195-3330
United States

Christian J. Murray

University of Houston - Department of Economics ( email )

Houston, TX 77204-5882
United States

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