# year    value 
 1980 5.067931 
 1981 4.235834 
 1982 4.442753 
 1983 5.316342 
 1984 4.215272 
 1985 4.111038 
 1986  4.41213 
 1987 4.582621 
 1988 5.428497 
 1989 4.998746 
 1990 5.594172 
 1991 4.970771 
 1992 4.386634 
 1993 4.328436 
 1994 5.214836 
 1995 5.492651 
 1996 4.333368 
 1997 4.786417 
 1998 5.434743 
 1999 5.383452 
 2000 4.313793 
 2001 5.668272 
 2002 4.979649 
 2003 5.167684 
 2004 5.376873 
 2005 5.677508 
 2006  5.52518 
 2007 5.477854 
 2008  5.60953 
 2009 5.060315 
 2010 5.718078 
 2011 5.328824 
 2012  5.34894 
 2013 5.590175 
 2014 5.627853 
 2015 5.527125 
 2016 5.166844 
 2017 5.508242 
 2018 5.451506