Year	Percent
1960	14.29656
1961	18.74476
1962	18.11322
1963	18.00483
1964	18.22142
1965	16.96955
1966	18.13332
1967	18.37151
1968	25.07982
1969	27.53694
1970	26.42461
1971	27.67497
1972	29.24444
1973	32.31958
1974	41.02315
1975	35.03614
1976	37.09169
1977	43.56701
1978	36.72704
1979	35.18273
1980	38.35635
1981	51.50593
1982	43.43327
1983	51.7804
1984	49.18999
1985	39.23034
1986	32.6505
1987	28.95604
1988	29.59418
1989	30.90776
1990	32.18561
1991	30.91765
1992	30.74157
1993	29.37256
1994	39.06695
1995	37.32746
1996	32.76459
1997	33.5521
1998	34.26227
1999	35.05417
2000	37.21679
2001	37.76429
2002	38.96524
2003	38.73646
2004	39.76872
2005	42.42418
2006	43.09745
2007	47.84522
2008	52.42943
2009	41.27457
2010	40.26636
2011	44.66521
2012	48.90039
2013	49.16338
2014	47.2985
2015	46.25932
2016	43.93411
2017	42.75393