Year	Percent
1967	9.17075
1968	9.15917
1969	8.66432
1970	7.76879
1971	7.14233
1972	11.77432
1973	13.52683
1974	13.68056
1975	10.85362
1976	10.72161
1977	9.28464
1978	9.24069
1979	10.69262
1980	12.48728
1981	12.31717
1982	9.94559
1983	11.91851
1984	11.07039
1985	10.42335
1986	11.90075
1987	13.23483
1988	13.58642
1989	13.88311
1990	15.53831
1991	16.99694
1992	17.3593
1993	16.30648
1994	16.28252
1995	16.70997
1996	16.9031
1997	16.08195
1998	16.48479
1999	15.3535
2000	13.44132
2001	14.65954
2002	15.22362
2003	16.71897
2004	15.6669
2005	15.6895
2006	14.13396
2007	13.21461
2008	12.38231
2009	12.39575
2010	13.51627
2011	13.96667
2012	12.39666
2013	13.27715
2014	12.24258
2015	10.60441
2016	9.14573
2017	8.23544