Year years 1960 42.29965553186857 1961 44.83717450930028 1962 48.17992536864728 1963 48.616751864491434 1964 49.156658815085976 1965 48.83937300316741 1966 49.62928811793648 1967 50.17189608121249 1968 50.90139009075543 1969 51.3929534364962 1970 51.74690999805753 1971 51.69353003313585 1972 52.98010114358677 1973 53.64895171554079 1974 54.11242240034206 1975 54.69191224889845 1976 55.26853634855807 1977 55.79349996639663 1978 56.21035518872754 1979 56.68126556611739 1980 57.10290569012954 1981 57.46574194823195 1982 57.83680433502171 1983 58.15919036500319 1984 58.53459978920066 1985 58.910129796806494 1986 59.32144220803312 1987 59.664662445149446 1988 59.86961262797877 1989 60.312956323740856 1990 60.52500650346736 1991 60.78043165869443 1992 61.10914826077281 1993 61.40022365332809 1994 61.748257158701456 1995 61.978175022050074 1996 62.248907180353775 1997 62.585611903470095 1998 62.85968206246633 1999 63.2966393468946 2000 63.63784928541805 2001 63.954565975490254 2002 64.28430775985917 2003 64.59134690993778 2004 64.8133158975438 2005 65.18070840608938 2006 65.5189144232952 2007 65.750411312238 2008 65.94002915029601 2009 66.32267459710978 2010 66.6219387392832 2011 66.96018946538022 2012 67.25327576145008 2013 67.56001108970126 2014 67.92309925063587 2015 68.2247761038965 2016 68.48776363516922 2017 68.67317072229984 2018 68.98150567842588 2019 69.17251681936226 2020 68.42058398150388 2021 67.40794505480652 2022 68.11256842812948