# year    value 
 1980 12.39153 
 1981 12.28995 
 1982 12.17954 
 1983 12.18532 
 1984 11.82645 
 1985 12.13387 
 1986 12.09807 
 1987 12.56057 
 1988  12.6219 
 1989 12.27107 
 1990 12.58797 
 1991 12.32177 
 1992  12.0754 
 1993 12.13304 
 1994 12.54537 
 1995 12.47582 
 1996 12.16589 
 1997  12.3977 
 1998 13.05322 
 1999 13.05263 
 2000 12.62036 
 2001 12.91912 
 2002 13.06312 
 2003 12.66069 
 2004 13.08536 
 2005 12.74381 
 2006 13.25176 
 2007  13.2236 
 2008 12.79026 
 2009 13.17144 
 2010 13.10182 
 2011 12.65711 
 2012 12.41755 
 2013 13.01844 
 2014 12.70788 
 2015 13.11925 
 2016 13.33122 
 2017 13.25944 
 2018 13.02677