# year    value 
 1980 9.425066 
 1981 10.04184 
 1982 8.432163 
 1983 9.096944 
 1984 8.668588 
 1985 8.425832 
 1986  9.77431 
 1987 9.528837 
 1988 9.552614 
 1989 9.263609 
 1990 9.400228 
 1991 9.177625 
 1992 9.747379 
 1993 8.631647 
 1994 10.01407 
 1995  9.92984 
 1996 9.798545 
 1997 9.299968 
 1998  9.40228 
 1999 9.506639 
 2000 9.593273 
 2001   9.7989 
 2002  9.37354 
 2003 10.18878 
 2004 9.730423 
 2005 9.774551 
 2006 10.02031 
 2007  9.89325 
 2008 9.338196 
 2009 9.373559 
 2010 9.498581 
 2011 9.168666 
 2012 10.45919 
 2013 9.525472 
 2014 10.42007 
 2015 10.77998 
 2016 10.56076 
 2017 10.21479 
 2018  10.2643