Year	Percent
1967	17.39216
1968	17.08133
1969	17.34085
1970	15.27732
1971	16.00583
1972	17.08613
1973	16.88687
1974	13.53295
1975	15.52187
1976	13.36338
1977	15.58858
1978	15.91784
1979	15.47453
1985	12.84285
1986	16.63634
1987	20.15162
1988	18.5008
1989	21.33887
1990	19.09127
1991	17.11453
1992	20.81833
1993	15.46445
1994	20.67475
1995	21.17208
1996	19.39175
1997	20.66446
1998	19.80432
1999	17.89321
2000	17.17566
2001	20.48952
2002	15.74577
2003	20.81184
2004	21.62902
2005	20.88189
2006	21.19245
2007	23.87414
2008	24.23647
2009	22.021
2010	24.02575
2011	19.72345
2012	17.18306
2013	17.79907
2014	17.63093
2015	17.40749
2016	17.40354
2017	19.94165