Year years 1960 39.85606735535527 1961 40.14182908422675 1962 40.65319092815938 1963 40.938064338546894 1964 41.38030057261757 1965 41.54163267399007 1966 41.775967920777134 1967 41.81410762767292 1968 42.34081340452971 1969 42.6393372796769 1970 43.199400197146794 1971 43.8150815682265 1972 44.1169464473273 1973 44.985131460122595 1974 45.419197581624076 1975 45.86477198575972 1976 46.45769799290285 1977 47.008695715993866 1978 47.28835338236283 1979 47.630776726597716 1980 47.77564171165028 1981 48.037607414840714 1982 48.20014535382841 1983 47.97832133742723 1984 47.74843907666038 1985 47.894678330090535 1986 48.41844319898444 1987 47.978546330554806 1988 47.538169886863976 1989 48.68847961037613 1990 48.72872621177603 1991 48.64986201162135 1992 48.56316302137059 1993 49.057588197397074 1994 49.90104942388661 1995 49.71632546157431 1996 49.72926762911527 1997 49.970104707669805 1998 49.63320214860726 1999 50.7283999451106 2000 51.473936000652195 2001 51.9215614271429 2002 52.368116135500856 2003 52.88379279020072 2004 53.339801647140824 2005 53.93977917223587 2006 54.578575353319906 2007 55.08678013802482 2008 55.613654377498584 2009 56.30800351254707 2010 56.811968283324376 2011 57.38710651746939 2012 57.86979270053935 2013 58.330059291371185 2014 58.752196541557815 2015 59.119371262141314 2016 59.52391506277527 2017 59.95061134692821 2018 60.35483877540976 2019 60.7216573709725 2020 60.249531838873345 2021 59.87258063232004 2022 60.50302117203396