Year	Percent
1965	31.4741
1966	30.05464
1967	33.89513
1968	32.63158
1969	27.49004
1970	25.96754
1971	22.33607
1972	24.20213
1973	28.96104
1974	28.5078
1975	24.85929
1976	27.00422
1977	28.74433
1978	32.07292
1979	31.13289
1980	25.94208
1981	25.63386
1982	23.93353
1983	22.62809
1984	22.50857
1985	21.34579
1986	25.20705
1987	31.92634
1988	35.26982
1989	37.38374
1990	36.82849
1991	36.22451
1992	36.1292
1993	36.83498
1994	36.00901
1995	37.74272
1996	36.35384
1997	37.64956
1998	37.67271
1999	36.74126
2000	39.39411
2001	39.47126
2002	39.28223
2003	38.32618
2004	39.82485
2005	39.78172
2006	39.82493
2007	40.41704
2008	39.59144
2009	39.90976
2010	37.70556
2011	36.77749
2012	37.2391
2013	35.85749
2014	35.80422
2015	35.73692
2016	35.49865