# year    value 
 1979    7.159 
 1980  7.68689 
 1981  7.86522 
 1982 7.031034 
 1983 6.631012 
 1984 8.033184 
 1985 7.604977 
 1986 7.080314 
 1987 7.590116 
 1988 7.347026 
 1989 7.053213 
 1990 7.004283 
 1991 7.388563 
 1992 7.251771 
 1993 7.285745 
 1994 7.675677 
 1995  7.51089 
 1996 7.327456 
 1997 7.676966 
 1998  8.00915 
 1999 8.330417 
 2000 8.021998 
 2001  8.10358 
 2002 8.206692 
 2003 7.514776 
 2004 8.874653 
 2005   7.8129 
 2006 8.123025 
 2007 8.608824 
 2008 8.737697 
 2009 8.421833 
 2010 8.509168 
 2011 7.661438 
 2012  7.90022 
 2013 8.742599 
 2014 8.152605 
 2015  8.43113 
 2016 9.069841 
 2017 8.360601 
 2018 9.130472