# year    value 
 1980 -27.82147 
 1981 -26.43063 
 1982 -29.06185 
 1983 -28.07031 
 1984 -28.21398 
 1985 -28.49356 
 1986 -26.31694 
 1987 -28.21693 
 1988 -28.28537 
 1989 -27.23291 
 1990 -29.36905 
 1991 -28.48977 
 1992 -27.49366 
 1993 -27.27651 
 1994 -29.05486 
 1995 -27.2025 
 1996 -27.66668 
 1997 -27.81101 
 1998 -28.30791 
 1999 -28.97527 
 2000 -27.57427 
 2001 -27.71272 
 2002 -28.24946 
 2003 -26.77511 
 2004 -27.58515 
 2005 -28.2019 
 2006 -27.62867 
 2007 -26.75649 
 2008 -27.41064 
 2009 -28.82544 
 2010 -27.60435 
 2011 -27.82551 
 2012 -27.27743 
 2013  -28.596 
 2014 -26.26228 
 2015 -25.55787 
 2016 -25.20188 
 2017 -26.34813 
 2018 -25.72785