Year	Percent
1970	22.41176
1971	21.83951
1972	26.52796
1973	18.91289
1974	21.65983
1975	19.01248
1976	20.68756
1977	19.87191
1978	22.026
1979	18.40971
1980	20.87381
1981	19.15867
1982	19.91045
1983	21.03805
1984	19.33185
1985	20.63322
1986	23.45972
1987	25.33983
1988	30.55142
1989	23.64906
1990	28.28516
1991	30.67588
1992	31.71246
1993	29.00847
1994	27.84108
1995	28.20159
1996	27.71731
1997	25.77387
1998	29.3864
1999	24.34586
2000	24.73395
2001	25.29794
2002	25.00504
2003	24.65548
2004	22.43326
2005	20.2931
2006	21.4568
2007	19.45881
2008	18.7564
2009	22.79501
2010	19.43897
2011	20.6469
2012	23.4323
2013	25.10493
2014	26.86013
2015	33.13046
2016	34.16687
2017	40.63561
2018	39.00988
2019	40.74104
2020	36.64186
2021	27.82215