Year	Percent
1960	38.48453
1961	38.30701
1962	37.85878
1963	38.49363
1964	38.68111
1965	35.41478
1966	36.2672
1967	33.41198
1968	31.59393
1969	32.01766
1970	30.51187
1971	30.59941
1972	31.9021
1973	29.39852
1974	30.82462
1975	28.86616
1976	29.01546
1977	28.42249
1978	30.1206
1979	29.37995
1980	28.44634
1981	29.80398
1982	27.51931
1983	27.61483
1984	28.49884
1985	33.90417
1986	29.36043
1987	27.81633
1988	28.5467
1989	27.62771
1990	27.95002
1991	29.79327
1992	28.80981
1993	30.23105
1994	32.94777
1995	33.21722
1996	36.37917
1997	33.73878
1998	36.56356
1999	27.25229
2000	24.91404
2001	26.92043
2002	26.37245
2003	25.96098
2004	23.38144
2005	26.77092
2006	25.22898
2007	21.83949
2008	27.31428
2009	23.20485
2010	24.14339
2011	23.04365
2012	23.75601
2013	23.64109
2014	23.69377
2015	22.6465
2016	21.71472
2017	20.58632
2018	20.99747
2019	18.22052
2020	17.85329
2021	17.23251
2022	18.4976