Year	Percent
1960	10.5041
1961	10.10228
1962	9.20191
1963	7.93761
1964	8.56055
1965	8.84735
1966	9.2656
1967	8.60685
1968	7.67637
1969	6.85996
1970	6.78135
1971	8.10213
1972	8.30309
1973	6.66427
1974	5.68892
1975	6.58294
1976	8.43881
1977	9.83057
1978	7.6008
1979	7.26881
1980	7.22472
1981	6.46461
1982	6.28803
1983	5.88756
1984	7.14647
1985	7.46874
1986	8.56961
1987	8.79361
1988	8.48176
1989	8.30497
1990	8.23652
1991	9.25622
1992	9.20579
1993	8.03366
1994	7.50221
1995	7.00303
1996	5.01956
1997	5.00655
1998	5.39423
1999	5.29404
2000	5.08296
2001	4.06242
2002	4.06503
2003	4.09478
2004	3.75827
2005	3.92221
2006	3.71205
2007	3.55057
2008	3.42443
2009	3.69713
2010	3.47828
2011	3.62618
2012	3.27493
2013	3.47338
2014	3.94662
2015	3.7094
2016	4.19909
2017	4.28097
2018	3.92744
2019	3.98332
2020	4.04199
2021	3.64535
2022	3.54439