1981 2.6 1982 3.2 1983 3.6 1984 1.3 1985 2.6 1986 1.7 1987 3.8 1988 3.5 1989 4.8 1990 4.5 1991 4.3 1992 4.4 1993 4.9 1994 3.8 1995 3.7 1996 3.0 1997 4.2 1998 4.1 1999 4.0 2000 4.0 2001 2.9 2002 4.3 2003 3.3 2004 4.8 2005 3.9 2006 2.7 2007 5.4 2008 3.8 2009 4.9 2010 4.0