# year    value 
 1980 23.33382 
 1981 23.28144 
 1982 23.73017 
 1983 23.71062 
 1984 23.77487 
 1985 23.67746 
 1986 23.58005 
 1987 24.22394 
 1988 24.07942 
 1989  23.6411 
 1990 23.94388 
 1991  23.6451 
 1992 23.39977 
 1993 23.56656 
 1994  24.1446 
 1995  24.1379 
 1996 23.67677 
 1997 24.21978 
 1998 23.72101 
 1999 23.75982 
 2000 23.71601 
 2001 23.84632 
 2002 24.16957 
 2003 24.07376 
 2004 24.20175 
 2005 23.56546 
 2006 23.97812 
 2007 23.93052 
 2008 24.07735 
 2009 24.27212 
 2010 23.93016 
 2011 24.25779 
 2012 24.53418 
 2013 23.89237 
 2014  24.7014 
 2015 24.35985 
 2016 24.01571 
 2017 24.08247 
 2018 24.22854