# year    value 
 1980 12.95786 
 1981 12.71758 
 1982 12.41222 
 1983 13.26193 
 1984 12.06381 
 1985 12.51035 
 1986 12.38161 
 1987 12.73703 
 1988 12.24557 
 1989 11.97251 
 1990 12.23868 
 1991 13.07714 
 1992 13.19683 
 1993 12.89915 
 1994  13.0195 
 1995  12.6384 
 1996 12.44932 
 1997 13.24112 
 1998 13.16874 
 1999 11.98858 
 2000 12.19865 
 2001 12.08021 
 2002 12.75762 
 2003 12.43535 
 2004   12.366 
 2005 12.32646 
 2006  12.5244 
 2007 11.91575 
 2008 11.88634 
 2009 13.15684 
 2010 12.75103 
 2011 12.26711 
 2012 12.77152 
 2013 12.32363 
 2014 12.32536 
 2015 13.42149 
 2016 12.61654 
 2017 12.78838 
 2018 13.00384