# year    value 
 1979 6.978762 
 1980 7.117316 
 1981 6.976626 
 1982 6.706486 
 1983 6.610658 
 1984 6.801983 
 1985 6.817263 
 1986 6.724756 
 1987 7.378485 
 1988 7.394268 
 1989 6.730419 
 1990 7.274835 
 1991 7.070386 
 1992 6.726973 
 1993 7.014443 
 1994  7.41537 
 1995 7.097198 
 1996 6.921716 
 1997 6.891526 
 1998 7.854597 
 1999 7.825442 
 2000 7.234621 
 2001  7.69516 
 2002 7.651416 
 2003 7.477756 
 2004 7.611392 
 2005 7.342494 
 2006 8.001879 
 2007 7.872529 
 2008 7.472124 
 2009 7.836086 
 2010 7.939431 
 2011 7.421602 
 2012 7.151305 
 2013 7.831582 
 2014 7.604005 
 2015 7.982027 
 2016 8.419917 
 2017 8.227469 
 2018 7.899105