# year    value 
 1980 16.18629 
 1981  16.2278 
 1982 16.14221 
 1983 16.23164 
 1984 16.08348 
 1985 15.90658 
 1986 15.87361 
 1987 16.43931 
 1988 16.10258 
 1989 16.34813 
 1990 16.27555 
 1991 16.24883 
 1992 15.49946 
 1993 15.93858 
 1994 15.94588 
 1995 16.01084 
 1996 15.90461 
 1997 15.61855 
 1998 16.18066 
 1999 16.74747 
 2000 15.66651 
 2001 16.14017 
 2002 16.18429 
 2003 16.20623 
 2004 16.35703 
 2005 16.46718 
 2006 16.51946 
 2007 16.08352 
 2008 16.67603 
 2009 16.72185 
 2010 16.02168 
 2011 16.28994 
 2012 16.59911 
 2013 16.60587 
 2014 16.58317 
 2015 16.41647 
 2016 16.89702 
 2017 17.00825 
 2018 17.08826