# year    value 
 1979 6.963009 
 1980 7.644569 
 1981 6.607649 
 1982  7.13915 
 1983 7.697581 
 1984 7.205607 
 1985 6.715774 
 1986 6.866141 
 1987 7.552838 
 1988 7.705908 
 1989 7.438084 
 1990  7.93153 
 1991 7.324924 
 1992 6.974441 
 1993 7.355381 
 1994   7.7668 
 1995 7.821289 
 1996   7.3327 
 1997 6.828946 
 1998 8.730428 
 1999 8.078827 
 2000 7.388879 
 2001 8.293971 
 2002 7.567924 
 2003 8.028198 
 2004 7.454509 
 2005 8.036992 
 2006 8.413352 
 2007 7.959609 
 2008 7.934127 
 2009 7.861192 
 2010 8.202297 
 2011   8.2427 
 2012 7.448708 
 2013 7.926962 
 2014 8.169523 
 2015 8.663334 
 2016 8.637937 
 2017 8.672827 
 2018 7.370352