Year years 1960 47.59978445181542 1961 50.5186424494781 1962 54.325187816211916 1963 54.78984279611284 1964 55.30827139930785 1965 55.179350558414264 1966 55.76314995331648 1967 56.24385103409963 1968 56.94423600759255 1969 57.34283532468515 1970 57.889844937382854 1971 58.49194060141899 1972 58.94967554581507 1973 59.617017551712244 1974 60.237376186579155 1975 60.86624130191525 1976 61.42611880260285 1977 62.05840972338739 1978 62.5914425592383 1979 63.13589886277868 1980 63.64646626679782 1981 64.16644300290973 1982 64.65437622803984 1983 65.12782029022843 1984 65.50209239969445 1985 65.89852047448039 1986 66.39883247788698 1987 66.76417989166725 1988 67.10646198047378 1989 67.44666721550249 1990 67.67314475071524 1991 67.85765404981835 1992 68.17549127829739 1993 68.50613584215232 1994 68.7499524995221 1995 69.09502129674605 1996 69.3684851924605 1997 69.7148125377098 1998 70.1171327722227 1999 70.28278057664566 2000 70.69597352152269 2001 71.2309138300556 2002 71.55518273821188 2003 71.8497623706152 2004 72.10309204790794 2005 72.5602950742946 2006 72.94058505649045 2007 73.25631517345482 2008 73.45985279975511 2009 73.85378621135926 2010 74.13679035049115 2011 74.4768525415786 2012 74.82271096824641 2013 75.14337512541988 2014 75.45935743065952 2015 75.72840802044081 2016 76.02256876317551 2017 76.28702236891687 2018 76.53860046629785 2019 76.73149547871553 2020 76.13267236061905 2021 74.85788191123487 2022 75.5641237370072