Year	Percent
1977	20.35482
1978	17.65231
1979	17.564
1980	19.12488
1981	17.6975
1982	19.13326
1983	19.51014
1984	17.89097
1985	17.35172
1986	18.94735
1987	19.73521
1988	23.82432
1989	23.26031
1990	24.95107
1991	23.66535
1992	23.26462
1993	22.4106
1994	20.72591
1995	21.75186
1996	21.22816
1997	20.37947
1998	21.69433
1999	23.43506
2000	26.91818
2001	30.4037
2002	28.49763
2003	24.56123
2004	22.89858
2005	22.41537
2006	23.45
2007	23.76161
2008	23.09159
2009	24.86741
2010	24.90122
2011	23.25821
2012	20.99253
2013	21.89881
2014	23.30906
2015	24.16126
2016	24.28618
2017	25.453