Year	Percent
1971	29.34174
1972	34.32914
1973	33.86687
1974	40.09542
1975	35.63768
1976	44.18639
1977	36.11439
1978	38.19313
1979	41.35731
1980	38.29209
1981	22.7043
1982	22.40978
1983	18.42415
1984	16.10454
1985	17.10288
1986	18.05922
1987	19.9285
1988	16.87188
1989	20.90856
1990	26.67707
1991	19.93837
1992	24.64998
1993	36.10313
1994	38.32137
1995	36.57615
1996	38.64839
1997	45.08069
1998	52.80253
1999	51.97953
2000	41.92522
2001	32.24676
2002	27.88286
2003	23.76906
2004	21.83389
2005	19.11145
2006	19.40764
2007	23.42508
2008	24.82836
2009	30.10059
2010	26.05637
2011	20.7829
2012	24.36599
2013	20.27366
2014	18.53272
2015	18.68556
2016	20.99421