# year    value 
 1980 9.405225 
 1981 10.62637 
 1982 9.099196 
 1983 8.721972 
 1984 9.605999 
 1985 10.75213 
 1986 11.07457 
 1987 10.77694 
 1988 10.37957 
 1989 10.82496 
 1990 10.34974 
 1991 9.781536 
 1992 11.52827 
 1993 10.20885 
 1994 11.01314 
 1995  8.94047 
 1996 9.591241 
 1997 9.637971 
 1998 9.268996 
 1999 9.421045 
 2000 11.16205 
 2001 10.48863 
 2002 9.172027 
 2003 10.18057 
 2004  11.4379 
 2005 10.40255 
 2006 11.06018 
 2007 11.26301 
 2008 9.563906 
 2009 10.12967 
 2010 9.796695 
 2011 9.578549 
 2012 12.20785 
 2013 10.05902 
 2014 10.42562 
 2015 11.21537 
 2016 11.49286 
 2017 11.31439 
 2018 11.01166