# year    value 
 1980     0.25 
 1981      0.2 
 1982    -0.08 
 1983    -0.28 
 1984    -0.12 
 1985     0.09 
 1986     0.31 
 1987    -0.08 
 1988     0.41 
 1989     0.12 
 1990     0.41 
 1991     0.39 
 1992    -0.15 
 1993    -0.38 
 1994     0.93 
 1995     0.36 
 1996      0.4 
 1997     0.54 
 1998     0.96 
 1999     0.65 
 2000        1 
 2001     1.21 
 2002     1.14 
 2003     0.94 
 2004     0.67 
 2005     0.95 
 2006     1.16 
 2007     1.25 
 2008     1.09 
 2009     0.64 
 2010     1.06 
 2011     1.04 
 2012     1.29 
 2013      1.1 
 2014     0.98 
 2015     1.49 
 2016     1.44 
 2017     1.62 
 2018     1.57