Year	Percent
1971	9.67493
1972	10.72685
1973	13.71125
1974	9.89995
1975	7.02239
1976	9.80442
1977	25.62906
1978	29.46492
1979	35.14953
1980	15.28258
1981	15.71746
1982	14.44626
1983	11.10454
1984	17.68169
1985	13.30813
1986	9.22967
1987	6.50985
1988	4.75515
1989	5.19567
1990	7.61875
1991	11.00514
1992	15.1305
1993	23.95909
1994	25.99946
1995	25.15576
1996	23.91538
1997	25.19418
1998	22.05719
1999	16.63202
2000	12.23107
2001	15.16345
2002	16.84448
2003	21.75817
2004	19.00681
2005	24.20297
2006	23.8926
2007	24.84528
2008	16.03203
2009	27.4485
2010	33.18248
2011	26.12559
2012	19.88603
2013	19.07724
2014	19.42786
2015	16.62393
2016	12.89095