# year    value 
 1980 4.936105 
 1981 5.076315 
 1982  5.05296 
 1983 4.841856 
 1984 4.897617 
 1985 5.054018 
 1986 5.041439 
 1987   5.0091 
 1988 5.095388 
 1989 5.102391 
 1990 5.143921 
 1991  5.16903 
 1992 4.913533 
 1993 4.976898 
 1994 5.059536 
 1995 5.126914 
 1996 5.121092 
 1997 5.218918 
 1998 5.268533 
 1999 5.380669 
 2000 5.277183 
 2001 5.493528 
 2002 5.445474 
 2003 5.482849 
 2004 5.380732 
 2005 5.469596