# year    value 
 1980 3.224165 
 1981 4.589611 
 1982 3.649851 
 1983 3.639187 
 1984 3.741466 
 1985 3.797276 
 1986 3.953931 
 1987  3.55773 
 1988 3.850679 
 1989 4.561882 
 1990 4.717428 
 1991 3.559866 
 1992 4.171829 
 1993 4.081055 
 1994 4.503871 
 1995 3.923301 
 1996 3.844841 
 1997 4.596694 
 1998 4.590078 
 1999 4.054566 
 2000 4.986522 
 2001 4.828666 
 2002 4.614982 
 2003 4.167007 
 2004 4.955837 
 2005 4.575934 
 2006 4.557072 
 2007 5.074448 
 2008 5.367142 
 2009  4.78525 
 2010 4.096744 
 2011 4.486911 
 2012 4.702945 
 2013  4.77609 
 2014  5.02361 
 2015 5.093592 
 2016 5.456101 
 2017 5.399142 
 2018 5.606958