Year	Percent
1975	20.87007
1976	17.27367
1977	25.10786
1978	23.01174
1979	21.13341
1981	24.82102
1982	23.44449
1983	23.20232
1984	20.44976
1985	19.42533
1986	18.76369
1987	14.55205
1988	14.32261
1989	13.87661
1990	13.18837
1991	14.90412
1992	18.48023
1993	18.76418
1994	19.04743
1995	17.62304
1996	17.46295
1997	15.96465
2002	13.40776
2003	13.34994
2004	13.83598
2005	14.06864
2006	15.82951
2007	15.34985
2008	15.32052
2009	15.66136
2010	14.13008
2011	14.00864
2012	12.3849
2013	13.49806
2014	12.22014
2015	12.51921