Year	% (national estimate)
1960	42.8
1961	43.4
1962	43.3
1963	42.9
1964	43.3
1965	44
1966	46.5
1967	47.6
1968	48.5
1969	50.4
1970	51.3
1971	51.1
1972	53
1973	54.9
1974	56.6
1975	57.2
1976	58
1977	59.6
1978	61.7
1979	62.5
1980	61.9
1981	61.9
1982	62
1983	61.9
1984	62.8
1985	63.7
1986	64.3
1987	64.6
1988	64.5
1989	64.4
1990	62.9
1991	61.7
1992	61.8
1993	62
1994	62.742
1995	62.485
1996	62.393
1997	62.928
1998	63.341
1999	62.909
2000	63
2001	62.002
2002	61.055
2003	59.229
2004	58.663
2005	58.575
2006	57.861
2007	57.196
2008	56.498
2009	55.228
2010	53.554
2011	53.276
2012	53.201
2013	53.48
2014	53.581
2015	53.794
2016	53.787
2017	54.266
2018	54.521
2019	55.146
2020	53.212
2021	54.526
2022	54.644
2023	55.918