# year    value 
 1980 13.20439 
 1981 13.55459 
 1982 12.77198 
 1983 12.53966 
 1984 13.39309 
 1985 13.03867 
 1986  12.8286 
 1987 13.08519 
 1988 12.90149 
 1989  12.8257 
 1990 12.84276 
 1991 12.89315 
 1992 12.82199 
 1993 12.86084 
 1994 13.33868 
 1995 13.14072 
 1996 12.84124 
 1997 13.55655 
 1998 13.60038 
 1999 13.73129 
 2000 13.94671 
 2001 13.97352 
 2002 13.97008 
 2003 13.12002 
 2004 14.46645 
 2005 13.69828 
 2006 13.90354 
 2007 14.17094 
 2008 14.62843 
 2009 14.15436 
 2010 13.96476 
 2011 13.40246 
 2012 13.86349 
 2013 14.40188 
 2014 13.87161 
 2015 14.04106 
 2016 14.75532 
 2017 14.19932 
 2018 14.89655