# year    value 
 1980 3.002277 
 1981 3.002049 
 1982 2.837189 
 1983 2.766122 
 1984 2.884812 
 1985 2.884998 
 1986 2.943232 
 1987 3.033422 
 1988 3.089911 
 1989 3.119483 
 1990 3.178841 
 1991 3.093323 
 1992 2.791096 
 1993 2.963816 
 1994 2.948667 
 1995 3.057687 
 1996 3.183174 
 1997 3.283192 
 1998 3.274696 
 1999 3.332816 
 2000 3.310129 
 2001 3.410497 
 2002 3.474052 
 2003 3.398961 
 2004 3.455836 
 2005 3.519518