# year    value 
 1979 12.08552 
 1980 12.60465 
 1981 11.33776 
 1982 12.09422 
 1983 12.42033 
 1984 11.93018 
 1985 11.56726 
 1986 11.73921 
 1987 12.17317 
 1988 12.54312 
 1989 12.25314 
 1990  12.7456 
 1991 12.20895 
 1992 11.63763 
 1993 11.86699 
 1994 12.44855 
 1995 12.68806 
 1996 12.09834 
 1997 11.95275 
 1998 13.44292 
 1999  12.8459 
 2000 12.08335 
 2001 13.05116 
 2002 12.50039 
 2003 12.67074 
 2004 12.47819 
 2005 12.98834 
 2006 13.41006 
 2007 12.75729 
 2008 12.88964 
 2009 12.61886 
 2010 13.07501 
 2011 12.92107 
 2012 12.22784 
 2013 12.87815 
 2014 12.88994 
 2015 13.22215 
 2016 13.00597 
 2017 13.29474 
 2018 12.30731