# year    value 
 1980     0.51 
 1981     0.75 
 1982     0.32 
 1983     0.73 
 1984     0.24 
 1985    -0.19 
 1986     0.45 
 1987     0.51 
 1988     0.71 
 1989     0.65 
 1990     0.59 
 1991     0.65 
 1992     0.63 
 1993     0.64 
 1994     0.26 
 1995     1.12 
 1996     0.48 
 1997     0.69 
 1998      1.1 
 1999     1.19 
 2000     0.95 
 2001      0.6 
 2002     1.27 
 2003     0.81 
 2004     1.17 
 2005     0.79 
 2006     0.85 
 2007     1.53 
 2008     0.65 
 2009     0.92 
 2010     0.88 
 2011     0.61 
 2012     0.69 
 2013     0.85 
 2014     0.94 
 2015     1.43 
 2016     2.04 
 2017     1.58 
 2018     1.34