Year	Percent
1967	18.83317
1968	20.88765
1969	21.25589
1970	19.53205
1971	19.31836
1972	23.18866
1973	26.51366
1974	31.4559
1975	23.24447
1976	25.08076
1977	25.03362
1978	27.65369
1979	25.71581
1980	43.80118
1981	43.03581
1982	45.36402
1983	46.75658
1984	45.29916
1985	43.26562
1986	43.2918
1987	41.47176
1988	40.84752
1989	40.63205
1990	41.07059
1991	39.12032
1992	41.69434
1993	39.40014
1994	40.71863
1995	38.48869
1996	37.83412
1997	36.63988
1998	37.53717
1999	37.33447
2000	37.26264
2001	35.87225
2002	35.2873
2003	37.26405
2004	36.54711
2005	34.79101
2006	34.59125
2007	35.9501
2008	36.91657
2009	34.24427
2010	35.45322
2011	36.72796
2012	34.21872
2013	36.8544
2014	36.27982
2015	36.09712
2016	36.60143
2017	36.70437