# year    value 
 1979 7.157328 
 1980 6.587062 
 1981   7.2435 
 1982 7.792034 
 1983 7.752716 
 1984 6.791223 
 1985 6.990276 
 1986 7.274072 
 1987 7.290163 
 1988 7.898336 
 1989  7.97888 
 1990 8.026132 
 1991 7.126455 
 1992 8.024272 
 1993 7.673662 
 1994 8.957289 
 1995  7.77611 
 1996 7.146879 
 1997 8.223079 
 1998 8.022557 
 1999 8.038169 
 2000 8.715809 
 2001 8.236221 
 2002  8.76389 
 2003 8.625816 
 2004 8.074232 
 2005 7.692554 
 2006 8.520662 
 2007 8.926481 
 2008 8.677647 
 2009 8.680653 
 2010 7.725519 
 2011 9.063139 
 2012 8.687853 
 2013 8.392589 
 2014 9.453247 
 2015  9.39858 
 2016 8.957301 
 2017 8.895816 
 2018 9.573343