Year	Percent
1971	13.03703
1972	17.0579
1973	27.50476
1974	34.05651
1975	37.12558
1976	42.08246
1977	48.43611
1978	62.35442
1979	68.74892
1980	74.1124
1981	65.63304
1982	54.07613
1983	45.91887
1984	43.30745
1985	28.57813
1986	21.18863
1987	19.69908
1988	13.88973
1989	18.15569
1990	31.01078
1991	45.76709
1992	33.89649
1993	39.08142
1994	48.48873
1995	42.26886
1996	40.78923
1997	33.87767
1998	30.95485
1999	28.78221
2000	24.86821
2001	25.22137
2002	19.00854
2003	14.46475
2004	15.83386
2005	15.6234
2006	17.79504
2007	22.97419
2008	22.86743
2009	27.69969
2010	26.20106
2011	31.9786
2012	31.12878
2013	37.38304
2014	42.35567
2015	36.82833
2016	42.15332