Year	Percent
1980	11.54928
1981	17.13926
1982	19.0304
1983	20.95852
1984	21.26311
1985	19.37511
1986	19.77319
1987	25.56449
1988	22.58722
1989	23.41715
1990	24.21838
1991	25.05426
1992	26.92564
1993	28.76641
1994	28.71907
1995	32.62371
1996	32.68176
1997	32.50219
1998	31.74705
1999	34.41831
2000	35.21764
2001	37.09847
2002	37.39547
2003	38.11468
2004	36.30719
2005	35.92837
2006	37.70358
2007	44.05219
2008	43.19856
2009	41.96599
2010	42.77832
2011	40.98293
2012	41.61801
2013	42.35118
2014	40.55266
2015	41.34637
2016	41.45649
2017	39.04547