# year    value 
 1980 8.164292 
 1981 8.325552 
 1982 8.147669 
 1983 7.779236 
 1984 8.167718 
 1985 8.131692 
 1986 8.310541 
 1987 8.286339 
 1988 8.384054 
 1989  8.51946 
 1990 8.339014 
 1991 8.166362 
 1992 8.034321 
 1993 8.101988 
 1994 8.486542 
 1995 8.511197 
 1996 8.726444 
 1997 8.746158 
 1998 8.872488 
 1999 8.703444 
 2000 9.020616 
 2001 9.226557 
 2002 8.813148 
 2003 9.112888 
 2004 9.010097 
 2005 9.069147