Year	Percent
1960	47.88764
1961	48.3168
1962	47.55031
1963	47.54606
1964	46.66628
1965	46.6163
1966	46.12936
1967	46.14271
1968	46.15301
1969	45.41038
1970	46.33788
1971	48.56529
1972	48.95007
1973	47.22092
1974	40.22736
1975	48.88133
1976	45.52542
1977	47.07134
1978	49.3481
1979	47.5176
1980	47.41254
1981	49.15212
1982	49.51871
1983	47.68678
1984	46.35769
1985	41.42918
1986	42.03111
1987	40.69052
1988	38.06791
1989	39.35157
1990	39.00486
1991	39.90207
1992	41.14007
1993	41.3469
1994	40.6836
1995	39.78747
1996	50.98906
1997	51.75426
1998	53.81974
1999	54.71051
2000	54.09561
2001	54.86507
2002	54.5288
2003	53.72508
2004	51.7233
2005	50.52024
2006	47.2097
2007	48.48961
2008	53.56901
2009	53.95332
2010	52.77835
2011	53.48735
2012	55.6342
2013	56.94649
2014	56.68851
2015	57.87587
2016	58.52678
2017	57.59058