Year	% (national estimate)
1960	40.97
1970	35.93
1976	48.22
1977	44.17
1978	44.66
1979	44.98
1980	33.58
1981	43.44
1982	43.19
1983	40.13
1984	41.69
1985	42.31
1986	38.73
1987	39.61
1988	42.02
1990	43.03
1991	46.46
1992	43.54
1993	47.06
1995	43.8
1996	46.1
1997	48.13
1998	49.45
1999	47.08
2000	44.28
2002	45.15
2003	46.44
2004	47.06
2005	49.05
2006	44.19
2007	40.87
2008	37.11
2010	31
2011	30
2012	31