# year    value 
 1980 8.892759 
 1981 8.514414 
 1982  8.36401 
 1983 9.053479 
 1984 8.382107 
 1985 8.343959 
 1986 8.537952 
 1987 8.845434 
 1988 9.188526 
 1989 8.834343 
 1990 9.152107 
 1991  8.98825 
 1992 8.355192 
 1993 8.722123 
 1994  9.13412 
 1995 9.450964 
 1996 8.541295 
 1997 8.955635 
 1998 9.271144 
 1999 9.139064 
 2000   8.5507 
 2001 9.457354 
 2002 9.199697 
 2003 9.396643 
 2004 9.374245 
 2005 9.720108 
 2006 9.655707 
 2007 9.615732 
 2008 9.618523 
 2009 9.441842 
 2010 9.770477 
 2011 9.442251 
 2012 9.619989 
 2013 9.588351 
 2014 9.701764 
 2015 9.983226 
 2016  9.77716 
 2017  9.79608 
 2018 9.767278