Year	Percent
1971	17.48292
1972	44.37139
1973	96.05826
1974	75.61756
1975	69.13262
1976	78.07364
1977	48.94762
1978	41.33941
1979	77.25182
1980	53.36399
1981	28.15511
1982	17.12337
1983	13.70958
1984	11.92585
1985	14.31298
1986	12.06662
1987	12.84303
1988	12.63978
1989	9.72402
1990	9.0008
1991	8.49341
1992	9.80562
1993	14.78167
1994	13.05004
1995	17.79642
1996	16.73886
1997	7.85775
1998	6.73629
1999	11.07679
2000	8.36162
2001	3.2686
2002	3.30966
2003	2.95597
2004	4.7295
2005	2.18639
2006	3.14894
2007	2.85837
2008	1.43316
2009	13.69197
2010	11.07532
2011	9.02712
2012	6.64687
2013	5.79237
2014	4.52574
2015	4.97352
2016	4.57645