# year    value 
 1980 9.019652 
 1981 11.35175 
 1982 10.08879 
 1983 10.91965 
 1984 9.057605 
 1985 10.23683 
 1986 10.70986 
 1987 8.817252 
 1988 10.66616 
 1989 11.74734 
 1990 11.71214 
 1991 10.03081 
 1992 11.33407 
 1993 11.27372 
 1994 11.65484 
 1995 10.38905 
 1996 10.16294 
 1997 10.97009 
 1998 11.11535 
 1999 11.83517 
 2000 12.32028 
 2001 11.86698 
 2002 11.83497 
 2003 11.97247 
 2004 10.38055 
 2005 10.95096 
 2006 10.62317 
 2007 12.96373 
 2008 11.31588 
 2009 12.40228 
 2010 10.86006 
 2011 12.63128 
 2012 12.26243 
 2013 10.38939 
 2014 12.36623 
 2015 11.78158 
 2016 11.34324 
 2017  12.4741 
 2018 12.66645