year trend year trend year trend year trend 1957.5 0.233 1958.5 0.201 1959.5 0.296 1960.5 -0.018 1961.5 -0.108 1962.5 -0.218 1963.5 -0.283 1964.5 -0.380 1965.5 -0.389 1966.5 -0.270 1967.5 -0.252 1968.5 -0.012 1969.5 0.012 1970.5 0.183 1971.5 0.220 1972.5 0.416 1973.5 0.313 1974.5 0.538 1975.5 0.448 1976.5 0.293 1977.5 0.322 1978.5 0.280 1979.5 -0.167 1980.5 -0.339 1981.5 -0.204 1982.5 -0.126 1983.5 0.067 1984.5 0.227 1985.5 0.298 1986.5 0.176 1987.5 0.145 1988.5 0.381 1989.5 0.200 1990.5 -0.010 1991.5 0.044 1992.5 0.127 1993.5 0.273 1994.5 0.456 1995.5 0.454 1996.5 0.479 1997.5 0.412 1998.5 0.130 1999.5 0.303 2000.5 0.516 2001.5 0.647 2002.5 0.609 2003.5 0.652 2004.5 0.232 2005.5 0.004 2006.5 0.060 2007.5 0.142