# year    value 
 1979 9.143954 
 1980 9.118808 
 1981 9.178125 
 1982 9.164623 
 1983 9.706868 
 1984 8.785347 
 1985 8.548427 
 1986 8.535641 
 1987 8.659812 
 1988  9.27226 
 1989 9.201014 
 1990 9.733187 
 1991 9.356731 
 1992 8.695936 
 1993 7.735677 
 1994 10.02139 
 1995 9.516387 
 1996 8.791311 
 1997 9.338231 
 1998 9.561904 
 1999 9.737903 
 2000 8.935556 
 2001 10.05693 
 2002 9.396194 
 2003 9.745947 
 2004  10.2591 
 2005 10.60249 
 2006 10.06584 
 2007 10.01874 
 2008 10.14904 
 2009 10.01321 
 2010 10.33312 
 2011 10.04842 
 2012 10.01155 
 2013 10.22336 
 2014 9.401785 
 2015  10.2334 
 2016 9.813634 
 2017 10.05544 
 2018 9.570408