# year    value 
 1980 13.15333 
 1981 11.95926 
 1982 12.62642 
 1983 12.97288 
 1984 12.33954 
 1985 12.21318 
 1986 12.27705 
 1987 12.65885 
 1988 13.06613 
 1989 12.83243 
 1990 13.27877 
 1991 12.61768 
 1992  12.1089 
 1993 12.28485 
 1994 12.80356 
 1995 13.12282 
 1996 12.53474 
 1997 12.34413 
 1998 13.75409 
 1999 13.36826 
 2000 12.47977 
 2001 13.41676 
 2002 12.99567 
 2003 13.10484 
 2004 13.03046 
 2005 13.52595 
 2006  13.8585 
 2007 13.20809 
 2008 13.41463 
 2009 13.11564 
 2010 13.56018 
 2011 13.31396 
 2012  12.6324 
 2013 13.29827 
 2014 13.33878 
 2015 13.34485 
 2016  13.1777 
 2017 13.54477 
 2018 12.81052