| Year | Value | | 2022 | 60.811085267704 | | 2021 | 60.955894359539 | | 2020 | 61.256605978657 | | 2019 | 61.656391434555 | | 2018 | 61.517864071148 | | 2017 | 60.800299837281 | | 2016 | 60.838816378609 | | 2015 | 59.842051523981 | | 2014 | 57.836831505026 | | 2013 | 57.280452201251 | | 2012 | 57.096212495909 | | 2011 | 56.891589067458 | | 2010 | 56.929572909291 | | 2009 | 57.268265636458 | | 2008 | 57.661688539494 | | 2007 | 58.104915131789 | | 2006 | 58.602087069991 | | 2005 | 59.047652705127 | | 2004 | 59.155200347716 | | 2003 | 59.002972154255 | | 2002 | 58.851674641148 | | 2001 | 58.699967966645 | | 2000 | 58.546199521319 | | 1999 | 58.388315497753 | | 1998 | 58.224753015041 | | 1997 | 58.052601580046 | | 1996 | 57.869522895901 | | 1995 | 57.559408949374 | | 1994 | 56.850684843027 | | 1993 | 55.870455871726 | | 1992 | 55.43266118856 | | 1991 | 55.523702874207 | | 1990 | 55.776810843148 | | 1989 | 55.981616397732 | | 1988 | 56.205918503743 | | 1987 | 56.445544665622 | | 1986 | 56.702655819618 | | 1985 | 56.847761352056 | | 1984 | 56.900549397845 | | 1983 | 56.935890434947 | | 1982 | 56.917118240981 | | 1981 | 56.895690217453 | | 1980 | 56.764912609531 | | 1979 | 56.465779109601 | | 1978 | 56.069188021133 | | 1977 | 55.607689069735 | | 1976 | 55.103778177621 | | 1975 | 54.915337436747 | | 1974 | 55.089351394472 | | 1973 | 55.277493567928 | | 1972 | 55.481212757925 | | 1971 | 55.705026236297 | | 1970 | 56.038720157053 | | 1969 | 56.531241756881 | | 1968 | 57.130419590173 | | 1967 | 57.822233525744 | | 1966 | 58.599590070438 | | 1965 | 59.076366184026 | | 1964 | 59.16912149918 | | 1963 | 59.247218747473 | | 1962 | 59.311457204051 | | 1961 | 59.276060724705 | | 1960 | 59.134620107067 |
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