Year Percent 1980 99 1981 99 1982 99 1983 99 1984 99 1985 99 1986 99 1987 99 1988 99 1989 99 1990 99 1991 99 1992 99 1993 99 1994 99 1995 99 1996 99 1997 99 1998 99 1999 99 2000 99 2001 99 2002 99 2003 99 2004 99 2005 99 2006 99 2007 99 2008 99 2009 99 2010 99 2011 99