Year	Percent
1960	11.1218
1961	11.21555
1962	16.73307
1963	16.00757
1964	16.37627
1965	31.91993
1966	29.67337
1967	37.42763
1968	47.83864
1969	50.88817
1970	39.74074
1971	38.4409
1972	34.68905
1973	44.67728
1974	41.76347
1975	46.18825
1976	43.40979
1977	42.31502
1978	52.46597
1979	48.26758
1980	47.3381
1981	47.82639
1982	42.14008
1983	38.65596
1984	41.21063
1985	42.86461
1986	37.27548
1987	40.56111
1988	34.4682
1989	35.07959
1990	34.6423
1991	33.36792
1992	31.98579
1993	35.65016
1994	35.40661
1995	35.26302
1996	34.2256
1997	32.57432
1998	31.17944
1999	35.16163
2000	35.66449
2001	33.70536
2002	35.81574
2003	35.41618
2004	39.05235
2005	40.90574
2006	40.65705
2007	41.44222
2008	39.15951
2009	30.70037
2010	32.89973
2011	35.50328
2012	36.05197
2013	31.45387
2014	30.8046
2015	28.25848
2016	28.17868