# year    value 
 1980 12.47544 
 1981 12.17402 
 1982 12.49429 
 1983 12.81202 
 1984 11.99265 
 1985 12.26271 
 1986 12.44686 
 1987 12.87091 
 1988 12.28038 
 1989 12.33681 
 1990 12.29292 
 1991 12.52722 
 1992 12.47557 
 1993 12.57093 
 1994 12.90604 
 1995 12.63332 
 1996 12.14049 
 1997 13.01664 
 1998 12.85865 
 1999 12.05678 
 2000 12.11215 
 2001 12.25855 
 2002 12.41925 
 2003 12.54232 
 2004 12.56316 
 2005 12.28051 
 2006 12.70534 
 2007 11.90881 
 2008 12.31075 
 2009 12.64925 
 2010 12.39175 
 2011  12.3199 
 2012 12.69368 
 2013 12.37139 
 2014 12.67208 
 2015 12.99646 
 2016 12.76538 
 2017 12.83521 
 2018 12.44743