1. A new approach to decomposition of economic time series into permanent and transitory components with particular attention to measurement of the ‘business cycle’
2. (1991a), ‘Near observational equivalence of unit root and stationary processes: theory and implications’. Unpublished manuscript, Johns Hopkins University.
3. (1991b), ‘Spurious regressions with an AR(1) correction’. Unpublished manuscript. Johns Hopkins University.
4. and , (1991). ‘Pitfalls and opportunities: what macroeconomists should know about unit roots’, NBER Macroeconomics Annual, 141–201.
5. Unit roots in real GNP: Do we know, and do we care?