# year    value 
 1979  20.3469 
 1980 19.90387 
 1981 19.75026 
 1982  20.1955 
 1983 19.56143 
 1984  19.2222 
 1985 19.55297 
 1986 20.02847 
 1987  20.3703 
 1988 19.57014 
 1989 20.06472 
 1990 19.71457 
 1991 19.83685 
 1992 19.48378 
 1993 19.62028 
 1994 20.07953 
 1995 20.30025 
 1996 19.81666 
 1997 20.90537 
 1998 20.64351 
 1999  19.7103 
 2000  19.5666 
 2001 20.21627 
 2002 20.08534 
 2003  20.2566 
 2004 20.16971 
 2005 20.73604 
 2006 21.13166 
 2007 19.66936 
 2008 20.69776 
 2009 20.50137 
 2010 20.30435 
 2011 20.55573 
 2012 20.43874 
 2013 20.20928 
 2014 20.66597 
 2015 21.28791 
 2016 20.59626 
 2017 21.01724 
 2018 19.71626