Year years 1960 41.932149790433144 1961 46.45795784695048 1962 52.54846136023212 1963 53.142541091064984 1964 53.787583443509774 1965 53.80198856676049 1966 54.779226082433 1967 55.5173469769813 1968 56.055459677753795 1969 56.60648192694119 1970 57.209282271199484 1971 58.03355897920442 1972 58.71464377830671 1973 59.4838928297451 1974 60.1076305682931 1975 60.727454606905034 1976 61.39221803062353 1977 62.021890779978925 1978 62.54305441585065 1979 63.120953745113944 1980 63.608778674744606 1981 64.03985475025452 1982 64.5155833579602 1983 65.00281682686713 1984 65.46387536731825 1985 65.85675881573735 1986 66.30666478771246 1987 66.65671581837351 1988 66.91301247019899 1989 67.27009714699463 1990 67.43347405080236 1991 67.69250876308887 1992 68.10829900905446 1993 68.46142740879864 1994 68.74392027115863 1995 69.07923744898414 1996 69.35327994476502 1997 69.71124317081743 1998 70.10326800806556 1999 70.31627253299074 2000 70.68465927542053 2001 71.18969047493853 2002 71.49580682213512 2003 71.73397095903161 2004 71.8969323792615 2005 72.36715299498492 2006 72.6987776793454 2007 72.94776619195979 2008 73.11780999434924 2009 73.52450016074542 2010 73.79280897673155 2011 74.08269707896225 2012 74.3860750479773 2013 74.665309713948 2014 74.93692765301519 2015 75.14352788827692 2016 75.32332273568113 2017 75.46866926981716 2018 75.83723226460744 2019 76.04009150734498 2020 75.25385518504727 2021 74.89401587935987 2022 75.69569211262545