Year	Percent
1981	30.76699
1982	32.44917
1983	31.7616
1984	35.54775
1985	33.20554
1986	33.8642
1987	34.42839
1988	35.35196
1989	35.78117
1990	36.30579
1991	29.67222
1992	26.82844
1993	28.70818
1994	33.79767
1995	33.13147
1996	33.27439
1997	27.36944
1998	32.84028
1999	35.85854
2000	37.44799
2001	38.49928
2002	41.44314
2003	42.75016
2004	40.07366
2005	39.14495
2006	38.57264
2007	39.11411
2008	37.90013
2009	38.77082
2010	41.75507
2011	41.43006
2012	38.58152
2013	39.6701
2014	39.89201
2015	39.54571
2016	36.48145
2017	36.92207