Year	Percent
1960	33.24212
1961	33.29677
1962	33.0164
1963	34.16635
1964	33.45735
1965	33.28053
1966	37.45213
1967	36.04763
1968	36.8357
1969	36.75834
1970	33.23082
1971	33.8194
1972	32.77743
1973	31.54835
1974	35.67525
1975	35.26381
1976	29.04614
1977	29.76678
1978	40.55225
1979	49.80723
1980	51.06744
1981	47.18951
1982	38.04094
1983	35.6961
1984	55.57835
1985	55.86116
1986	48.84299
1987	46.60179
1988	43.63112
1989	43.6123
1990	48.06318
1991	50.20734
1992	62.27454
1993	44.08423
1994	55.5595
1995	51.27581
1996	45.24991
1997	40.58924
1998	38.43299
1999	39.03661
2000	38.79005
2001	35.56416
2002	32.76195
2003	36.61347
2004	37.54402
2005	35.27324
2006	40.13153
2007	39.72869
2008	41.94331
2009	34.47963
2010	31.33785
2011	30.37895
2012	30.19745
2013	30.60058
2014	31.25799
2015	29.91034
2016	31.36651
2017	31.54706