Year	Percent
1972	23.01849
1973	21.07158
1974	23.74607
1975	24.26561
1976	23.8007
1977	23.32577
1978	22.15422
1979	21.90378
1980	23.87607
1981	24.63943
1982	25.86614
1983	24.64853
1984	24.77763
1985	25.13357
1986	24.50068
1987	23.1588
1988	22.99075
1989	22.76227
1990	24.15129
1991	24.84714
1992	24.28032
1993	22.98109
1994	23.79709
1995	23.38854
1996	23.24289
1997	23.78132
1998	25.1246
1999	25.67968
2000	26.22898
2001	25.84914
2002	25.00835
2003	24.59342
2004	25.22206
2005	25.54736
2006	25.73855
2007	25.90968
2008	26.54625
2009	24.22741
2010	25.38761
2011	26.06183
2012	25.23794
2013	25.22519
2014	24.92093
2015	25.15972
2016	25.59712