Year	Percent
1990	21.40613
1991	20.71097
1992	19.93559
1993	19.52191
1994	19.91612
1995	18.75293
1996	19.53885
1997	19.65523
1998	19.6984
1999	17.40151
2000	17.82759
2001	18.70201
2002	19.29978
2003	19.17432
2004	19.66341
2005	21.30391
2006	21.78411
2007	22.92252
2008	21.69911
2009	22.48112
2010	23.59665
2011	22.56622
2012	22.45715
2013	23.33208
2014	23.42544