Year	Percent
1973	12.59214
1974	13.54284
1975	12.7559
1976	14.11996
1977	14.95878
1978	15.67368
1979	15.83207
1980	17.42573
1981	17.8432
1982	19.45246
1983	21.19826
1984	21.02519
1985	20.46361
1986	22.24978
1987	21.56347
1988	23.31732
1989	24.02693
1990	24.25775
1991	24.89063
1992	25.58219
1993	26.36189
1994	25.17705
1995	23.18364
1996	23.07212
1997	24.56451
1998	23.4776
1999	23.9271
2000	22.51138
2001	22.28118
2002	21.67999
2003	21.47393
2004	20.96754
2005	20.75262
2006	22.12405
2007	22.37674
2008	21.89234
2009	22.4353
2010	22.26325
2011	22.3006
2012	23.63177
2013	23.72805
2014	23.52199
2015	23.41691
2016	23.65956