Year	Percent
1972	11.44137
1973	12.49705
1974	13.62016
1975	12.43707
1976	12.18828
1977	12.30503
1978	12.65156
1979	11.88397
1980	11.61681
1981	12.3812
1982	12.65575
1983	12.04339
1984	11.72651
1985	10.84508
1986	10.69466
1987	11.20148
1988	11.18866
1989	10.4806
1990	10.07359
1991	10.62663
1992	12.02633
1993	12.09277
1994	11.64091
1995	12.3143
1996	12.70826
1997	12.676
1998	12.88682
1999	13.18857
2000	12.89478
2001	13.41377
2002	13.42807
2003	13.6448
2004	13.41779
2005	13.69854
2006	13.91075
2007	14.93465
2008	15.32646
2009	13.26216
2010	13.08809
2011	13.36523
2012	13.3192
2013	13.74171
2014	13.41666
2015	13.6571
2016	13.95135