Year	Percent
1972	23.83663
1973	25.60624
1974	28.09958
1975	27.6899
1976	27.5408
1977	29.55895
1978	28.08535
1979	29.36825
1980	29.44389
1981	30.36379
1982	30.28182
1983	28.10512
1984	28.34722
1985	29.37125
1986	30.18308
1987	33.27758
1988	32.47296
2001	28.55763
2002	28.20805
2003	29.24814
2004	29.25812
2005	30.31328
2006	31.96581
2007	30.08199
2008	31.49032
2009	29.59185
2010	26.06159
2011	25.55529
2012	26.82149
2013	26.64636
2014	26.8062
2015	27.40553
2016	27.18544