# year    value 
 1980 7.489621 
 1981 8.309958 
 1982 7.614538 
 1983 8.213747 
 1984 7.473245 
 1985 7.283332 
 1986  7.77983 
 1987 7.851405 
 1988 8.078787 
 1989 8.106958 
 1990 8.480941 
 1991 8.142026 
 1992 7.776431 
 1993 7.534034 
 1994 8.095788 
 1995 8.438608 
 1996 7.433011 
 1997 8.110359 
 1998 8.670809 
 1999 8.799151 
 2000 8.372135 
 2001 8.623828 
 2002 8.543546 
 2003 8.275359 
 2004 8.470193 
 2005 8.597046 
 2006 8.798794 
 2007 8.847548 
 2008 8.549062 
 2009 8.238297 
 2010 8.623837 
 2011 8.421996 
 2012 8.699711 
 2013 8.540348 
 2014 8.367633 
 2015 9.048279 
 2016 9.100427 
 2017   8.9823 
 2018 8.578012