Year	Percent
1971	2.13308
1972	75.74744
1973	59.82404
1974	57.58602
1975	88.25039
1976	49.04643
1977	69.45455
1978	62.51357
1979	64.34753
1980	46.93772
1981	30.3481
1982	40.54166
1983	34.0561
1984	35.55801
1985	27.86454
1986	36.56708
1987	43.06147
1988	33.29637
1989	31.95474
1990	34.3975
1991	30.82308
1992	27.31159
1993	19.57835
1994	22.28329
1995	14.24193
1996	10.02298
1997	8.20089
1998	8.85886
1999	8.63076
2000	7.68374
2001	7.03684
2002	6.06128
2003	8.76819
2004	8.73473
2005	6.97771
2006	5.47397
2007	6.27853
2008	7.35472
2009	4.03182
2010	4.38687
2011	4.07532
2012	5.71526
2013	6.18479
2014	4.90344
2015	4.6013
2016	3.15786
2017	4.16
2018	2.97715
2019	3.87248
2020	4.59066
2021	3.90413