Year	Percent
1960	16.14464
1961	17.33548
1962	15.68676
1963	15.13426
1964	17.35483
1965	16.8551
1966	17.61438
1967	18.16166
1968	16.93877
1969	16.0617
1970	15.02035
1971	15.98892
1972	18.1893
1973	18.60288
1974	21.58918
1975	18.36301
1976	20.23521
1977	19.95836
1978	19.8857
1979	22.57112
1980	24.11145
1981	23.84738
1982	22.91791
1983	20.11121
1984	21.90138
1985	23.21363
1986	25.6018
1987	28.89401
1988	33.01197
1989	34.92153
1990	34.13193
1991	35.96431
1992	36.97248
1993	36.81714
1994	38.24211
1995	41.53239
1996	39.01841
1997	48.23717
1998	57.93723
1999	56.4386
2000	64.84021
2001	63.25055
2002	60.64575
2003	61.52256
2004	65.97196
2005	68.40273
2006	68.67525
2007	68.87223
2008	71.4164
2009	64.43869
2010	66.48614
2011	70.85498
2012	69.77553
2013	68.11771
2014	69.28926
2015	68.7142
2016	68.11083