# year    value 
 1980 18.80302 
 1981 18.59526 
 1982 18.76292 
 1983 19.17493 
 1984 18.71808 
 1985 18.70278 
 1986  18.8342 
 1987 19.21159 
 1988 18.90263 
 1989 18.68931 
 1990 18.88115 
 1991 18.91121 
 1992 18.96535 
 1993 18.98469 
 1994 19.07395 
 1995  19.1259 
 1996 18.77116 
 1997 19.17786 
 1998 19.34813 
 1999  18.8322 
 2000 18.82804 
 2001 19.00172 
 2002 19.19736 
 2003 19.20994 
 2004 19.09384 
 2005 19.20117 
 2006 19.13077 
 2007 18.95991 
 2008 18.92448 
 2009 19.20335 
 2010 19.24901 
 2011 18.95613 
 2012 19.17145 
 2013 19.06132 
 2014 19.23512 
 2015 19.47353 
 2016 19.41251 
 2017 19.36329 
 2018 19.16488