Year	Percent
1960	20.17937
1961	17.77778
1962	18.18182
1963	17.64706
1964	15.69343
1965	13.48684
1966	18.125
1967	14.8368
1968	14.20911
1969	13.90887
1970	12.53133
1993	11.88041
1994	11.93855
1995	14.55232
1996	14.72006
1997	15.0205
1998	11.83377
1999	16.98373
2000	17.41525
2001	18.65986
2002	18.12452
2003	20.09876
2004	16.20761
2005	18.4657
2006	22.51698
2007	21.19729
2008	18.61673
2009	21.35991
2010	17.36766
2011	17.09791
2012	18.51134
2013	20.00892
2014	22.0945
2015	22.453
2016	22.70583
2017	22.91159