# year    value 
 1979 12.04989 
 1980 12.07985 
 1981 11.92459 
 1982 11.80969 
 1983 11.80331 
 1984 11.52271 
 1985 11.77295 
 1986 11.75785 
 1987 12.30617 
 1988 12.27967 
 1989 11.86503 
 1990 12.23752 
 1991 12.04315 
 1992 11.76037 
 1993 11.86024 
 1994 12.28954 
 1995 12.21619 
 1996 11.87314 
 1997 12.10967 
 1998 12.78883 
 1999 12.75657 
 2000 12.32123 
 2001 12.62782 
 2002 12.75249 
 2003 12.34916 
 2004 12.72138 
 2005 12.39308 
 2006 12.93939 
 2007 12.90886 
 2008 12.47038 
 2009 12.84832 
 2010 12.83187 
 2011 12.31584 
 2012 12.11532 
 2013 12.78994 
 2014 12.52387 
 2015 12.96655 
 2016 13.25519 
 2017 13.13042 
 2018 12.82078