Year years 1960 39.384638019324186 1961 39.704283881083626 1962 39.93535409468969 1963 40.283468313297206 1964 40.60988778003836 1965 40.844938396609116 1966 41.0360980419449 1967 41.003497820107896 1968 41.571927610043645 1969 41.79031334249522 1970 42.21369592163326 1971 42.6780206358183 1972 43.366275273519356 1973 43.92174339112007 1974 44.57037487145394 1975 45.31772744936131 1976 46.18790314430762 1977 46.96862277692277 1978 47.59242513405598 1979 48.00405722094504 1980 48.371227166396075 1981 48.60773305436053 1982 48.85878080892795 1983 49.117079620235685 1984 49.26131100156483 1985 49.39985629914762 1986 49.419545402508604 1987 49.73379940168596 1988 49.9586585534944 1989 50.14994578240085 1990 50.22901108639938 1991 50.16276386664746 1992 50.25557713843648 1993 50.3293033050882 1994 50.13066979838855 1995 50.232828067209795 1996 50.34940604717133 1997 50.50699538331107 1998 50.59224593680659 1999 51.00462819086272 2000 51.38252845554541 2001 51.676469048247284 2002 52.033916055639715 2003 52.52457948349551 2004 52.8903120879728 2005 53.39750452427889 2006 53.831594486257075 2007 54.24670473266834 2008 54.53774553806404 2009 55.077111186288384 2010 55.44060716898044 2011 55.92535594650018 2012 56.26070880302735 2013 56.61726350031962 2014 56.8809346833537 2015 57.16432389233239 2016 57.44860099512283 2017 57.842236001278856 2018 58.11324771678102 2019 58.545979044689304 2020 58.34623978556962 2021 58.099827740224086 2022 58.717472285813976