Year	Percent
1960	41.70436
1961	34.10257
1962	38.93884
1963	38.11002
1964	39.06172
1965	25.07024
1966	32.34251
1967	34.15723
1968	37.57326
1969	34.98171
1970	37.24532
1971	36.05287
1972	37.03291
1973	39.72807
1974	49.37209
1975	49.52088
1976	40.35304
1977	38.26688
1978	34.82042
1979	37.85171
1980	47.97165
1981	46.89693
1982	33.61376
1983	32.2663
1984	28.06281
1985	59.76696
1986	54.24523
1987	67.2217
1988	85.46205
1989	81.61107
1990	73.17272
1991	56.53193
1992	58.91018
1993	60.12518
1994	56.98216
1995	53.91995
1996	53.61345
1997	56.0648
1998	58.07352
1999	59.52768
2000	62.6041
2001	54.90382
2002	51.17518
2003	60.51874
2004	60.91861
2005	44.33672
2006	49.27978
2007	46.99423
2008	47.09233
2009	36.75086
2010	41.20341
2011	44.80206
2012	44.19631
2013	42.329
2014	41.12948
2015	38.29578
2016	37.79745
2017	37.33621