Year years 1960 67.47818369731247 1961 67.7506233291407 1962 67.624415009034 1963 67.95874723916727 1964 68.48063542173296 1965 68.4655231136565 1966 68.65290858702693 1967 68.66295934495814 1968 68.64020173667498 1969 68.43452353411466 1970 68.91063592614717 1971 69.10712082407656 1972 69.33052771057396 1973 69.44794548151614 1974 69.66369565455079 1975 69.61719083633281 1976 69.74442315757547 1977 69.9531282739114 1978 70.02507752097647 1979 70.13910040413626 1980 70.27080071804876 1981 70.55895169736282 1982 70.86508632347922 1983 70.90824866423719 1984 71.03059099749464 1985 71.2303995279343 1986 71.80311677758156 1987 72.02685069551795 1988 72.11514554431297 1989 72.23999254133385 1990 72.2257582064448 1991 72.1691378524204 1992 71.8906282124852 1993 71.53252982329641 1994 71.70356812512873 1995 71.79540250002701 1996 72.22514883184041 1997 72.63049910982583 1998 72.93990825912984 1999 72.88942797581014 2000 73.13222407214532 2001 73.39272537324324 2002 73.50306429159723 2003 73.61361044070284 2004 74.05467488354395 2005 74.1948289353497 2006 74.69334106292747 2007 75.05155897889593 2008 75.31299456894612 2009 75.70186847610314 2010 75.98653084553375 2011 76.45826323775073 2012 76.64226646799155 2013 76.98445179191556 2014 77.29442243562951 2015 77.2288167304908 2016 77.56267943400731 2017 77.7731288262557 2018 77.90651244772909 2019 78.18050698573892 2020 76.95248812517556 2021 76.66642379017874 2022 77.84131870047587