Year	% (national estimate)
1960	54.83
1970	62.5
1980	58.92
1983	38.27
1986	46.61
1988	48.13
1990	66.92
2002	43.6
2004	47.1
2005	51.4
2006	51.7
2007	44.8
2009	44.4
2011	46.1