Year	Percent
1960	20.79004
1961	22.66648
1962	20.4827
1963	23.4384
1964	22.07662
1965	28.82426
1966	29.40466
1967	24.85993
1968	25.97681
1969	28.33609
1970	28.18341
1971	27.1418
1972	29.43825
1973	30.35077
1974	28.47005
1975	38.67514
1976	40.0927
1977	34.22516
1978	32.36249
1979	32.57497
1980	34
1981	35.19241
1982	38.44645
1983	38.17494
1984	42.63117
1985	42.33622
1986	43.43343
1987	46.08851
1988	47.29093
1989	48.38199
1990	48.59342
1991	43.18917
1992	43.38038
1993	43.62932
1994	41.90575
1995	42.54367
1996	43.26591
1997	43.21494
1998	40.66154
1999	42.11331
2000	44.40019
2001	43.0014
2002	43.44262
2003	43.2315
2004	62.11741
2005	59.91196
2006	39.39873
2007	39.5181
2008	36.47698
2009	39.30515
2010	36.79706
2011	38.06767
2012	35.71675
2013	36.40839
2014	37.63941
2015	38.88044
2016	38.63519
2017	38.96918