# year    value 
 1980 2.590283 
 1981 2.723453 
 1982 2.651602 
 1983 2.405431 
 1984 2.544386 
 1985 2.555074 
 1986  2.55455 
 1987 2.643073 
 1988 2.801843 
 1989  2.67047 
 1990 2.852475 
 1991 2.753827 
 1992 2.466112 
 1993 2.598198 
 1994 2.549177 
 1995 2.628224 
 1996 2.802234 
 1997  2.88337 
 1998 2.936908 
 1999 2.934783 
 2000 3.018096 
 2001 3.023731 
 2002 3.143202 
 2003  3.08383 
 2004 3.067474 
 2005 3.218859