Christian E. Weber, "Cyclical Output, Cyclical Unemployment and Okun's
Coefficient:  A New Approach", Journal of Applied Econometrics,
Vol. 10, No. 4, 1995, pp. 433-445.

The data are in ASCII format in the file weber.dat, which has been
zipped.  They are arranged in a "format=prn" format for use in RATS.
The real GNP data for the U.S. are quarterly for the period
1948:1-1988:4.  These, along with the date of each observation appear
first in the data file.  The civilian unemployment rate data for the
U.S. are monthly for the period 1948:1-1988:12.  These, along with the
date of each observation, appear in the file after a one line break
following the real GNP series.  Quarterly observations of the
unemployment rate were obtained in RATS as simple averages of the three
monthly observations for the quarter.