Year years 1960 44.676095680227455 1961 47.395032094461435 1962 50.97036177506875 1963 51.419743328452306 1964 51.989968312853925 1965 51.937376075318056 1966 52.54871452091326 1967 53.138822884269885 1968 53.861638444977885 1969 54.35219743687944 1970 54.659557032604724 1971 55.009361306126166 1972 55.911781769724016 1973 56.60930140408133 1974 57.162672649047224 1975 57.774800327752374 1976 58.39052817148467 1977 59.069661482456986 1978 59.6307293788891 1979 60.20488001802485 1980 60.74581013248528 1981 61.25022575862414 1982 61.707088991603804 1983 62.07264012735306 1984 62.46266507946869 1985 62.8231924444396 1986 63.277921493456226 1987 63.67046813200307 1988 63.9389832429764 1989 64.33893066044511 1990 64.58012718474575 1991 64.68186758040402 1992 65.07393891414404 1993 65.40979832448113 1994 65.62082146501017 1995 65.88706043994722 1996 66.09004288878198 1997 66.45629980168664 1998 66.82159351136893 1999 67.15461371591452 2000 67.53397107103235 2001 68.03964439079841 2002 68.38094883549003 2003 68.75751975297673 2004 68.98652670053866 2005 69.43775550666747 2006 69.85433592136683 2007 70.15824433240023 2008 70.32705868602054 2009 70.78481625550431 2010 71.0918090116074 2011 71.46592516179926 2012 71.82061106634853 2013 72.1629107786407 2014 72.45666106021342 2015 72.72748418393542 2016 73.02859662819073 2017 73.31100745198808 2018 73.56021630176423 2019 73.7665356855976 2020 73.22668207711435 2021 72.2048235184431 2022 72.8031284268149