# year    value 
 1979 5.071301 
 1980 4.741482 
 1981 4.546946 
 1982 3.933923 
 1983 4.000248 
 1984 3.470728 
 1985 5.097249 
 1986 4.666648 
 1987 4.813629 
 1988 4.514428 
 1989 4.645458 
 1990  4.94351 
 1991 4.028374 
 1992 3.650405 
 1993 4.862252 
 1994 4.461582 
 1995 3.701731 
 1996 4.290802 
 1997 4.533341 
 1998 5.535878 
 1999 4.828036 
 2000  4.25427 
 2001 4.449327 
 2002 4.293277 
 2003 4.975641 
 2004 4.907712 
 2005 4.870842 
 2006 4.827137 
 2007 3.806059 
 2008 4.578543 
 2009 5.060408 
 2010 4.374588 
 2011 4.215648 
 2012 4.550356 
 2013  5.14654 
 2014 5.324507 
 2015 5.195458 
 2016 5.338667 
 2017 5.055955 
 2018 4.551212