Year	Percent
1981	24.97616
1982	25.69472
1983	26.31189
1984	26.97181
1985	27.17756
1986	28.27573
1987	28.3931
1988	28.81727
1989	38.79451
1990	41.21422
1991	34.33669
1992	34.69147
1993	30.04213
1994	31.42177
1995	32.8446
1996	23.65398
1997	28.52478
1998	22.60484
1999	22.30425
2000	22.19614
2001	21.94188
2002	22.48463
2003	25.21996
2004	28.33344
2005	32.4965
2006	38.69261
2007	37.73478
2008	30.85104
2009	30.05656
2010	33.19425
2011	31.33375
2012	30.77159
2013	30.50689
2014	31.49762
2015	31.04055
2016	33.67364
2017	32.96112