# year    value 
 1980 14.80208 
 1981 14.55945 
 1982 14.66129 
 1983 14.66684 
 1984 14.37706 
 1985 14.59642 
 1986  14.2294 
 1987 14.59215 
 1988 14.66756 
 1989 14.56434 
 1990 14.82498 
 1991  14.4507 
 1992 13.65487 
 1993 14.36119 
 1994 14.52905 
 1995 14.47271 
 1996 14.63844 
 1997 14.55384 
 1998 14.63476 
 1999 14.76879 
 2000 14.30051 
 2001 14.34653 
 2002 14.84728 
 2003 14.61732 
 2004 14.82926 
 2005 14.60568 
 2006 15.25233 
 2007 14.98175 
 2008 15.06974 
 2009  14.7474 
 2010 14.35185 
 2011 14.97476 
 2012 15.19143 
 2013 15.01394 
 2014 15.48654 
 2015 14.83122 
 2016 14.46704 
 2017 15.12784 
 2018 14.95456