Year years 1960 66.49132718838817 1961 66.84347470856835 1962 66.63138294608021 1963 66.94814916815554 1964 67.4157960571476 1965 67.51127640878762 1966 67.77615574159515 1967 67.72498520667308 1968 67.68787498383098 1969 67.43718765308252 1970 67.82176810039408 1971 67.89337613594986 1972 68.27706728711868 1973 68.37026118775874 1974 68.65725603059063 1975 68.61076086394613 1976 68.84503359697706 1977 69.10177435220443 1978 69.1678704224972 1979 69.4186269308555 1980 69.4115089411729 1981 69.75146917234017 1982 70.03652087454185 1983 70.06408776971743 1984 70.32584961039632 1985 70.40999336676427 1986 70.69094526566879 1987 70.90937374061507 1988 71.11087240788181 1989 71.1930158776079 1990 71.20366018052964 1991 71.27851321312235 1992 71.58180177056279 1993 71.75152316614974 1994 72.0113320956274 1995 72.1597852087045 1996 72.47556134052425 1997 72.84753343963304 1998 73.15736592621927 1999 73.42384647989815 2000 73.80659604681853 2001 74.20123956042606 2002 74.34104534982167 2003 74.46903631639042 2004 74.98009005062156 2005 75.1623352793022 2006 75.55994928779138 2007 75.83864575620616 2008 76.12803164451985 2009 76.37343300961406 2010 76.66701696259376 2011 77.16706490633476 2012 77.26907930537396 2013 77.62793746103121 2014 78.049480532526 2015 77.8275364082164 2016 78.1902182462582 2017 78.25890913286294 2018 78.35146684820278 2019 78.66590540503836 2020 77.73317288321088 2021 77.59144669143156 2022 78.18514670793152