Year	Percent
1990	39.34229
1991	29.76515
1992	34.90851
1993	31.25109
1994	25.53093
1995	25.3256
1996	25.05202
1997	29.66587
1998	29.19352
1999	27.97325
2000	21.40553
2001	20.58655
2002	19.37807
2003	22.48878
2004	21.03844
2005	20.36201
2006	21.66288
2007	20.58092
2008	19.53313
2009	18.9727
2010	21.04273
2011	21.59221
2012	21.08064
2013	22.14066
2014	22.82277
2015	23.95278
2016	24.71493
2017	23.10839