Year	Percent
1970	3.49505
1971	2.9973
1972	3.03739
1973	2.98482
1974	3.23768
1975	2.54505
1976	2.18279
1977	2.42303
1978	2.20035
1979	3.54166
1980	3.07171
1981	2.79352
1982	2.08549
1983	2.53182
1984	3.40972
1985	1.90447
1986	2.06426
1987	3.57888
1988	2.75248
1989	5.82608
1990	4.36509
1991	3.9697
1992	3.5654
1993	2.85187
1994	4.69723
1995	4.52103
1996	7.16548
1997	5.94354
1998	8.54106
1999	12.93091
2000	18.04965
2001	11.90049
2002	6.82422
2003	7.8062
2004	23.26756
2005	39.29585
2006	72.01219
2007	71.06271
2008	29.08986
2009	16.35335
2010	22.89596
2011	41.55567
2012	28.71418
2013	47.98195
2014	13.4558
2015	33.33705
2016	35.37524
2017	40.22209