Year	Percent
1971	19.28107
1972	24.07598
1973	40.19483
1974	61.87903
1975	25.35555
1976	20.14225
1977	9.74807
1978	11.92418
1979	16.4658
1980	17.44452
1981	17.23552
1982	12.68308
1983	8.62537
1984	6.13508
1985	4.32039
1986	3.01879
1987	3.81464
1988	2.93911
1989	4.41339
1990	2.76969
1991	3.25001
1992	3.08889
1993	2.25647
1994	1.95083
1995	3.75267
1996	5.92147
1997	8.18508
1998	2.17777
1999	1.51704
2000	2.0667
2001	1.73382
2002	3.25069
2003	1.34944
2004	1.65771
2005	3.03121
2006	12.16494
2007	12.0629
2008	9.9271
2009	10.39234
2010	10.72699
2011	17.84725
2012	29.30655
2013	28.32939
2014	18.04818
2015	21.7779
2016	22.13316