Year	Percent
1960	14.46366
1961	13.95947
1962	16.98796
1963	19.82464
1964	18.52797
1965	18.63514
1966	21.77255
1967	21.90058
1968	23.27153
1969	24.32592
1970	25.59769
1971	24.2086
1972	21.67666
1973	26.99595
1974	26.63503
1975	26.75041
1976	23.98528
1977	26.88476
1978	28.16387
1979	27.20523
1980	29.14192
1981	29.67531
1982	26.51654
1983	29.97528
1984	29.47311
1985	28.24458
1986	25.87231
1987	27.87471
1988	32.59089
1989	35.06612
1990	41.35376
1991	42.84138
1992	39.96395
1993	39.65599
1994	40.90773
1995	42.86265
1996	42.53268
1997	34.27481
1998	20.07138
1999	20.17336
2000	22.28259
2001	23.1124
2002	22.74421
2003	23.82929
2004	25.68146
2005	30.42076
2006	27.01162
2007	25.49598
2008	28.22645
2009	20.63643
2010	25.35665
2011	26.79148
2012	28.02417
2013	27.45709
2014	23.90537
2015	22.12768
2016	21.7435