Year	Percent
1971	23.75999
1972	42.0259
1973	56.76965
1974	48.07865
1975	28.55291
1976	24.5192
1977	10.80582
1978	10.97355
1979	16.23531
1980	17.2391
1981	12.61195
1982	14.2137
1983	13.42474
1984	11.30224
1985	8.90931
1986	8.84354
1987	8.86749
1988	9.54419
1989	15.14823
1990	15.4299
1991	13.00521
1992	13.27571
1993	11.43705
1994	13.03143
1995	18.82718
1996	22.10167
1997	23.30744
1998	21.21381
1999	24.00437
2000	20.13243
2001	17.62903
2002	21.89018
2003	24.67343
2004	23.37035
2005	30.23811
2006	29.97772
2007	29.41839
2008	25.35508
2009	26.87412
2010	28.57034
2011	28.77813
2012	35.17508
2013	33.57308
2014	31.65301
2015	27.85465
2016	26.11716