# year    value 
 1979 7.843578 
 1980 7.766693 
 1981 8.555621 
 1982 7.886283 
 1983 8.501009 
 1984  7.72882 
 1985 7.580245 
 1986 8.007762 
 1987 8.096201 
 1988 8.332032 
 1989 8.396761 
 1990 8.751551 
 1991 8.388902 
 1992 8.016876 
 1993 7.774997 
 1994 8.345314 
 1995 8.750247 
 1996 7.759208 
 1997  8.45985 
 1998  8.95071 
 1999 9.065164 
 2000  8.67578 
 2001 8.946665 
 2002 8.833686 
 2003 8.611492 
 2004 8.781966 
 2005 8.967699 
 2006 9.138928 
 2007 9.215705 
 2008 8.932963 
 2009 8.623525 
 2010 9.047738 
 2011 8.790145 
 2012 9.034389 
 2013  8.89914 
 2014 8.700249 
 2015  9.38139 
 2016 9.426554 
 2017 9.332308 
 2018 8.892989 
 2019 -1.797214