Year	Percent
1972	29.0073
1973	28.92176
1974	29.10847
1975	26.71838
1976	26.48584
1977	27.07075
1978	28.13562
1979	28.60342
1980	28.52585
1981	28.04778
1982	27.09919
1983	27.8065
1984	29.01039
1985	30.50282
1986	32.74337
1987	32.22171
1988	32.44584
1989	31.39666
1990	29.72461
1991	29.12938
1992	29.48601
1993	30.84809
1994	31.5603
1995	31.66082
1996	31.87981
1997	31.74704
1998	32.04661
1999	31.92656
2000	31.59411
2001	30.1672
2002	30.11719
2003	30.14078
2004	31.29221
2005	33.07177
2006	31.8603
2007	35.09301
2008	33.42154
2009	33.18383
2010	32.73723
2011	32.75348
2012	33.4464
2013	33.81975
2014	36.50029
2015	33.94595
2016	33.7391