Year Years 1970 9.87 1971 10.01 1972 10.14 1973 10.27 1974 10.4 1975 10.52 1976 10.63 1977 10.75 1978 10.86 1979 10.97 1980 11.07 1981 11.18 1982 11.28 1983 11.37 1984 11.47 1985 11.56 1986 11.65 1987 11.74 1988 11.83 1989 11.92 1990 12 1991 12.09 1992 12.17 1993 12.25 1994 12.34 1995 12.42 1996 12.51 1997 12.61 1998 12.71 1999 12.81 2000 12.92 2001 13.02 2002 13.13 2003 13.25 2004 13.36 2005 13.48 2006 13.6 2007 13.72 2008 13.84 2009 13.97 2010 14.1 2011 14.22 2012 14.35 2013 14.48 2014 14.61 2015 14.74