Year	Percent
1960	28.19333
1961	26.12903
1962	24.21479
1963	21.18182
1964	19.90291
1965	17.12142
1966	14.62451
1967	17.42021
1968	20.35294
1969	19.74013
1970	21.33687
1971	15.76
1972	20.71048
1973	21.45101
1974	18.32618
1975	19.364
1976	15.70641
1977	10.49897
1978	8.35795
1979	11.23237
1980	8.46635
1981	4.75587
1982	3.33831
1983	5.55592
1984	8.04403
1985	10.65449
1986	16.5761
1987	19.6626
1988	18.18338
1989	16.74264
1990	16.87789
1991	16.96355
1992	17.22596
1993	20.25392
1994	25.25864
1995	24.49645
1996	32.11218
1997	32.41029
1998	33.87135
1999	32.07834
2000	48.80226
2001	45.23302
2002	42.61625
2003	40.67904
2004	39.30333
2005	36.44922
2006	25.19212
2007	24.52509
2008	25.02946
2009	29.29187
2010	29.47672
2011	36.93661
2012	40.35922
2013	34.18908
2014	39.52356
2015	44.42404
2016	41.08037
2017	39.91525