Year	Percent
1972	44.09942
1973	52.60056
1974	69.39984
1975	67.59988
1976	56.40012
1977	55.79944
1978	54.90127
1979	61.28305
1980	47.67882
1981	30.64
1982	26.664
1983	27.7019
1984	40.75362
1985	29.65304
1986	31.95167
1987	29.32667
1988	22.83709
1989	23.60423
1990	20.23098
1991	21.92213
1992	20.99077
1993	20.67478
1994	19.41507
1995	20.15684
1996	13.44
1997	19.57714
1998	16.95269
1999	18.77383
2000	11.83586
2001	15.67598
2002	19.41418
2003	17.6222
2004	12.18223
2005	14.33852
2006	11.09966
2007	16.96955
2008	15.90645
2009	15.85968
2010	13.31581
2011	15.34524
2012	13.26216
2013	12.53729
2014	12.90078
2015	9.81598
2016	11.09641
2017	9.92433