# year    value 
 1980 5.269912 
 1981 7.735538 
 1982 6.194707 
 1983 7.078991 
 1984 5.112311 
 1985   6.4386 
 1986  7.22149 
 1987 5.075428 
 1988  7.00603 
 1989 7.923165 
 1990 7.829163 
 1991 6.212502 
 1992 7.516212 
 1993  7.39246 
 1994 8.111635 
 1995 6.640864 
 1996  6.58841 
 1997  7.47612 
 1998 7.360229 
 1999 8.092175 
 2000  8.57462 
 2001 8.435328 
 2002 8.213259 
 2003 8.337478 
 2004   6.7452 
 2005 7.541734 
 2006  7.28959 
 2007 9.579309 
 2008 7.785904 
 2009 8.897132 
 2010 7.279319 
 2011  9.16356 
 2012 8.654816 
 2013 6.998461 
 2014 8.644998 
 2015 8.462763 
 2016 7.879157 
 2017  9.07316 
 2018  9.08775