Year	Percent
1967	23.1873
1968	20.44524
1969	19.60678
1970	23.05292
1971	25.0366
1972	30.35847
1973	36.50223
1974	43.66995
1975	38.97012
1976	38.15514
1977	37.29252
1978	35.62947
1979	44.34478
1980	45.17376
1981	41.54903
1982	43.42577
1983	46.27137
1984	42.17141
1985	33.82832
1986	33.51049
1987	39.54452
1988	38.80656
1989	40.8718
1990	44.76321
1991	47.17035
1992	47.83914
1993	41.23306
1994	40.72425
1995	42.5697
1996	40.78952
1997	49.8737
1998	89.73703
1999	60.40227
2000	66.05098
2001	59.14416
2002	49.83425
2003	45.27959
2004	48.91946
2005	56.9216
2006	50.51881
2007	48.84438
2008	52.35779
2009	39.55519
2010	38.86169
2011	42.65905
2012	41.58789
2013	40.45706
2014	39.79183
2015	34.04307
2016	30.07712
2017	32.05179