Year	Percent
1960	20.20569
1961	20.43646
1962	18.07895
1963	17.64466
1964	17.4591
1965	17.66879
1966	20.43191
1967	18.46473
1968	21.16349
1969	20.47283
1970	20.33623
1971	19.24483
1972	17.93116
1973	18.09508
1974	21.40305
1975	17.0325
1976	17.66021
1977	18.71433
1978	18.25205
1979	18.16932
1980	19.06113
1981	20.62768
1982	20.50216
1983	19.90742
1984	18.9546
1985	19.02985
1986	18.00116
1987	19.06077
1988	20.64554
1989	18.49046
1990	18.50394
1991	15.94993
1992	16.71488
1993	21.28107
1994	25.53845
1995	25.79874
1996	22.15094
1997	20.92375
1998	19.72808
1999	12.88013
2000	14.89563
2001	16.03225
2002	17.25154
2003	18.68182
2004	19.441
2005	20.22102
2006	22.40309
2007	23.02701
2008	23.4872
2009	22.44004
2010	22.1262
2011	23.87634
2012	23.85252
2013	24.30848
2014	26.27846
2015	26.72048
2016	24.70494
2017	23.39487