# year    value 
 1980 8.054808 
 1981 7.948251 
 1982 7.759148 
 1983 7.694877 
 1984 7.606421 
 1985  7.82088 
 1986 7.704868 
 1987 8.219964 
 1988 8.286923 
 1989 7.860822 
 1990 8.230607 
 1991 7.937873 
 1992 7.608016 
 1993 7.780358 
 1994 8.194949 
 1995 8.006186 
 1996  7.81075 
 1997 7.885499 
 1998 8.684696 
 1999 8.698276 
 2000 8.178357 
 2001 8.545136 
 2002 8.595781 
 2003 8.339597 
 2004 8.604324 
 2005 8.388551 
 2006 8.913545 
 2007 8.786337 
 2008 8.371194 
 2009 8.814635 
 2010 8.766771 
 2011 8.344757 
 2012 8.121983 
 2013 8.658505 
 2014 8.339799 
 2015 8.685051 
 2016 8.944216 
 2017 8.836685 
 2018 8.645422