Year	Percent
1960	36.44438
1961	35.83823
1962	34.0027
1963	33.06552
1964	30.6342
1965	31.92325
1966	33.40021
1967	29.24378
1968	28.68293
1969	28.68472
1970	25.91588
1971	23.92438
1972	25.33804
1973	27.69023
1974	27.00573
1975	26.87108
1976	26.69553
1977	24.7831
1978	24.49816
1979	23.99356
1980	23.23988
1981	21.3571
1982	18.54845
1983	20.06017
1984	17.57386
1985	15.80937
1986	15.66415
1987	15.73344
1988	16.17806
1989	15.07529
1990	12.49963
1991	12.64983
1992	12.29734
1993	8.02583
1994	8.62755
1995	9.08122
1996	9.06342
1997	9.0649
1998	10.25923
1999	8.893
2000	8.49985
2001	8.57929
2002	8.69218
2003	9.44135
2004	9.29111
2005	9.19436
2006	9.40199
2007	9.34768
2008	10.07243
2009	9.78703
2010	10.52218
2011	11.59179
2012	11.5041
2013	11.32222
2014	10.08892
2015	8.87272
2016	8.47808
2017	8.40641
2018	8.20182
2019	8.12857
2020	8.70277
2021	8.70838
2022	8.81462