# year    value 
 1979 3.237549 
 1980 2.936248 
 1981 4.239059 
 1982 3.202173 
 1983 3.195585 
 1984 3.575763 
 1985 3.533299 
 1986 3.597043 
 1987  3.33834 
 1988 3.545209 
 1989 4.198476 
 1990 4.332636 
 1991 3.271991 
 1992  3.83353 
 1993 3.783581 
 1994  4.20118 
 1995 3.449337 
 1996 3.448467 
 1997 4.224038 
 1998 4.116159 
 1999 3.721171 
 2000 4.661456 
 2001 4.595173 
 2002 4.381006 
 2003 3.859105 
 2004 4.718293 
 2005  4.34841 
 2006 4.241827 
 2007 4.849275 
 2008 5.058947 
 2009 4.504345 
 2010 3.920441 
 2011 4.141587 
 2012 4.374306 
 2013 4.599136 
 2014 4.974367 
 2015 4.940709 
 2016 5.424608 
 2017 5.216957 
 2018   5.4418