# year    value 
 1980 0.05326766 
 1981 0.07053355 
 1982 -0.2049624 
 1983 -0.1126024 
 1984 -0.03379564 
 1985 0.01439428 
 1986 0.06077836 
 1987 0.1079696 
 1988 0.1464425 
 1989 0.274839 
 1990 0.2517774 
 1991 -0.04710529 
 1992 -0.08881222 
 1993 0.008846045 
 1994 0.08220691 
 1995 0.1890507 
 1996 0.2606096 
 1997 0.3309614 
 1998 0.3589905 
 1999 0.3763751 
 2000 0.4341958 
 2001 0.5665314 
 2002 0.5072348 
 2003 0.5284991 
 2004 0.5388701 
 2005 0.6316937