Year	Percent
1970	35.56334
1971	39.68902
1972	33.83764
1973	31.78928
1974	29.40246
1975	27.4184
1976	25.69963
1977	26.74009
1978	27.98348
1979	29.4568
1980	30.4919
1981	32.29612
1982	33.66614
1983	36.06068
1984	34.77649
1985	35.00258
1986	33.42339
1987	35.2594
1988	35.71284
1989	35.44598
1990	36.98307
1991	37.52058
1992	41.11435
1993	42.94984
1994	41.96569
1995	60.49841
1996	62.10302
1997	61.84001
1998	62.51232
1999	62.63461
2000	60.47919
2001	62.79095
2002	61.96065
2003	62.16864
2004	63.6444
2005	64.49894
2006	65.52979
2007	66.94225
2008	67.26549
2009	68.09859
2010	68.65369
2011	68.83518
2012	71.01095
2013	71.83045
2014	72.73338
2015	71.3917
2016	72.01831