Year	Percent
1975	28.81
1976	28.71
1977	28.72
1978	28.87
1979	28.92
1980	29.11
1981	29.52
1982	30
1989	39.06
2005	48.55
2006	47.32
2007	47.49
2008	47.53
2009	48.21
2010	47.61
2011	49.55
2012	49.63
2013	51.06
2014	51.48
2015	52.07