# year    value 
 1980 5.010267 
 1981 5.020752 
 1982 4.866027 
 1983 4.690964 
 1984 4.880401 
 1985  4.94614 
 1986  4.96056 
 1987 5.024423 
 1988 5.096569 
 1989 5.149953 
 1990  5.17788 
 1991 5.139607 
 1992 4.737895 
 1993  4.94174 
 1994 5.045381 
 1995 5.098622 
 1996 5.214977 
 1997 5.298747 
 1998  5.35397 
 1999 5.366206 
 2000  5.40831 
 2001 5.486541 
 2002 5.517394 
 2003 5.493773 
 2004 5.506724 
 2005 5.555368