Year	Percent
1977	11.5311
1978	10.37717
1979	11.58806
1980	13.06451
1981	13.31378
1982	10.41336
1983	10.22115
1984	10.91623
1985	11.72985
1986	12.9576
1987	13.80336
1988	14.23633
1989	15.2518
1990	13.91021
1991	14.56416
1992	13.48244
1993	12.70764
1994	12.52557
1995	12.69588
1996	12.24719
1997	12.51282
1998	12.6588
1999	13.51182
2000	13.82711
2001	12.87814
2002	13.04232
2003	13.19529
2004	13.05576
2005	14.52979
2006	18.46274
2007	17.75961
2008	19.15681
2009	19.48801
2010	16.13952
2011	14.4748
2012	14.1181
2013	15.5312
2014	15.80405
2015	16.11856
2016	17.51248
2017	18.15741