Year	Percent
1960	38.40206
1961	36.1668
1962	35.01529
1963	37.49083
1964	28.25306
1965	33.25198
1966	37.31183
1967	34.90276
1968	39.1581
1969	39.59368
1970	39.15737
1971	35.47431
1972	37.94163
1973	37.58242
1974	38.95991
1975	45.8939
1976	38.87255
1977	34.62912
1978	41.11403
1979	40.83285
1980	38.80211
1981	31.49535
1982	28.84554
1983	28.3229
1984	26.42615
1985	29.89871
1986	25.0488
1987	27.80988
1988	32.54301
1989	34.51757
1990	33.42077
1991	29.30731
1992	42.45583
1993	32.22197
1994	61.74514
1995	48.08842
1996	31.87667
1997	33.5854
1998	38.10502
1999	43.29369
2000	35.33498
2001	39.12718
2002	26.0402
2003	30.67199
2004	32.61799
2005	39.32683
2006	36.72613
2007	33.13272
2008	39.30901
2009	31.65442
2010	34.86046
2011	28.01069
2012	41.67819
2013	42.60933
2014	39.62504
2015	35.75475
2016	44.9408
2017	36.16703