Year	Percent
1975	4.98076
1976	6.14151
1977	6.24503
1978	6.4447
1979	6.86772
1980	6.23027
1981	10.3762
1982	10.26724
1983	9.71275
1984	13.2565
1985	22.28309
1986	22.27299
1987	20.34354
1988	24.34783
1989	19.72206
1990	15.33445
1991	9.7188
1992	12.43643
1993	16.50377
1994	21.34634
1995	16.13556
1996	21.12234
1997	12.82465
1998	12.26066
1999	14.9622
2000	14.12405
2001	8.93845
2002	7.64016
2003	6.56304
2004	7.97827
2005	6.93124
2006	4.42474
2007	3.20497
2008	2.60543
2009	3.09951
2010	2.4544
2011	2.39129
2012	1.75849
2013	3.01044
2014	2.97556
2015	4.23295