# year    value 
 1979 21.54885 
 1980 21.59411 
 1981 21.79548 
 1982 21.43331 
 1983 21.64058 
 1984 21.64321 
 1985 21.56621 
 1986 21.53068 
 1987 21.69278 
 1988 21.92807 
 1989  21.3541 
 1990 21.79807 
 1991 21.87861 
 1992 21.30399 
 1993 21.40423 
 1994 22.02018 
 1995 22.07878 
 1996  21.5955 
 1997 21.99461 
 1998 22.28973 
 1999 22.00788 
 2000 22.12728 
 2001 22.08825 
 2002  22.3115 
 2003 21.81405 
 2004 21.73598 
 2005 22.31187 
 2006 22.36532 
 2007 22.34133 
 2008  22.0953 
 2009 22.18837 
 2010 22.50472 
 2011 22.31399 
 2012 22.32474 
 2013 22.32882 
 2014 22.26126 
 2015 22.16432 
 2016 22.67325 
 2017 22.53638 
 2018 22.77309