Year	Percent
1960	33.65486
1961	34.0354
1962	35.2529
1963	34.19575
1964	31.83586
1965	31.31308
1966	28.03375
1967	28.40554
1968	29.28189
1969	26.25218
1970	26.02928
1971	25.25878
1972	25.83565
1973	25.3755
1974	24.09384
1975	22.35518
1976	20.11773
1977	18.70307
1978	18.20012
1979	16.02257
1980	16.11089
1981	15.76644
1982	15.92607
1983	16.90085
1984	18.61334
1985	18.87895
1986	20.81149
1987	21.34757
1988	22.0108
1989	22.40069
1990	20.52101
1991	20.86308
1992	18.92212
1993	23.40316
1994	22.14595
1995	21.91217
1996	20.75006
1997	20.10877
1998	17.47595
1999	17.57135
2000	15.40454
2001	12.65727
2002	11.23092
2003	10.8433
2004	9.69192
2005	9.48117
2006	9.40814
2007	9.35566
2008	8.96568
2009	9.91394
2010	9.73312
2011	9.60112
2012	8.64241
2013	8.76934
2014	9.12651
2015	9.45485
2016	9.51902
2017	9.32926
2018	8.94927
2019	8.80053
2020	9.84273
2021	9.41429
2022	8.84162