# year    value 
 1980 22.33867 
 1981 22.00096 
 1982 22.06867 
 1983 22.79031 
 1984 22.22397 
 1985 21.84554 
 1986 22.19798 
 1987 22.61905 
 1988 22.43472 
 1989 22.56075 
 1990 22.37324 
 1991 22.24306 
 1992 22.24752 
 1993 22.08525 
 1994  22.1906 
 1995 22.58458 
 1996 22.31479 
 1997 22.05971 
 1998 22.73284 
 1999  22.3095 
 2000  22.0106 
 2001 22.38403 
 2002 22.19641 
 2003 22.53762 
 2004 22.44761 
 2005 22.69118 
 2006 22.30459 
 2007 22.57549 
 2008 22.02238 
 2009 22.31846 
 2010 22.69423 
 2011 22.15176 
 2012 22.40526 
 2013    22.55 
 2014  22.5975 
 2015 22.43178 
 2016  23.1951 
 2017 22.90455 
 2018 22.47798