# year    value 
 1980 16.15989 
 1981 16.08194 
 1982 15.99492 
 1983 15.65444 
 1984 15.91745 
 1985 16.08994 
 1986 15.98456 
 1987 16.11754 
 1988 16.13118 
 1989 16.23264 
 1990 16.27094 
 1991 16.26911 
 1992 15.83605 
 1993 16.04485 
 1994 16.16918 
 1995 16.19525 
 1996  16.3631 
 1997 16.43379 
 1998 16.43869 
 1999 16.52328 
 2000 16.60342 
 2001 16.70172 
 2002 16.59154 
 2003  16.6194 
 2004 16.64374 
 2005 16.77385