Year Years 1970 6.98 1971 7.13 1972 7.28 1973 7.43 1974 7.58 1975 7.73 1976 7.88 1977 8.02 1978 8.17 1979 8.32 1980 8.47 1981 8.61 1982 8.76 1983 8.9 1984 9.05 1985 9.19 1986 9.33 1987 9.48 1988 9.62 1989 9.76 1990 9.9 1991 10.04 1992 10.18 1993 10.32 1994 10.46 1995 10.6 1996 10.76 1997 10.91 1998 11.07 1999 11.23 2000 11.39 2001 11.55 2002 11.71 2003 11.88 2004 12.04 2005 12.2 2006 12.37 2007 12.53 2008 12.69 2009 12.85 2010 13.01 2011 13.16 2012 13.32 2013 13.47 2014 13.62 2015 13.77