Year	Percent
1960	17.54126
1961	20.52495
1962	23.9038
1963	19.7405
1964	19.47981
1965	19.1524
1966	19.11747
1967	20.16048
1968	20.11382
1969	17.20047
1970	22.34374
1971	21.47772
1972	22.28222
1973	24.4713
1974	29.49295
1975	24.22894
1976	22.61285
1977	24.68532
1978	24.4582
1979	26.51655
1980	27.89897
1981	32.08599
1982	34.19056
1983	34.45516
1984	30.77742
1985	25.29414
1986	23.83086
1987	20.87293
1988	23.54316
1989	28.14689
1990	32.36033
1991	37.79075
1992	35.36279
1993	39.18394
1994	41.20229
1995	43.6401
1996	41.47936
1997	42.97308
1998	26.67488
1999	22.38185
2000	26.86749
2001	24.39822
2002	24.77741
2003	22.76339
2004	23.04952
2005	22.39642
2006	22.70356
2007	23.40969
2008	21.4584
2009	17.83573
2010	23.38654
2011	23.18826
2012	25.74862
2013	25.93711
2014	24.97761
2015	25.11361
2016	25.8743
2017	25.4621