Year	Percent
1970	16.14734
1971	20.3296
1972	17.50074
1973	16.42906
1974	13.07953
1975	11.36586
1976	11.7529
1977	19.62529
1978	22.97505
1979	18.02192
1980	28.2788
1981	27.6385
1982	31.24981
1983	33.73383
1984	36.94453
1985	39.60388
1986	44.59484
1987	48.11921
1988	46.40362
1989	39.66663
1990	33.35677
1991	34.51795
1992	36.28861
1993	38.66591
1994	51.99025
1995	44.37135
1996	45.15569
1997	45.34801
1998	35.54243
1999	40.33497
2000	43.42348
2001	57.84579
2002	55.37314
2003	47.04234
2004	39.98864
2005	34.99667
2006	38.61515
2007	38.84056
2008	38.39879
2009	43.7724
2010	39.31075
2011	37.02541
2012	39.06279
2013	41.4386
2014	43.4732
2015	46.68065
2016	47.79408