Year	% (national estimate)
1960	35.5
1961	35.4
1962	35.6
1963	35.8
1964	36.3
1965	37.1
1966	38.3
1967	39
1968	39.6
1969	40.7
1970	40.8
1971	40.4
1972	41
1973	42
1974	42.6
1975	42
1976	43.08273225602626
1977	44.29014467347219
1978	46.114083058354154
1979	47.27235204196505
1980	47.575363778779334
1981	47.97366530378082
1982	47.587768144695644
1983	47.88902815908856
1984	49.325881543908224
1985	50.276776219271945
1986	51.29207218795406
1987	52.37961725724954
1988	53.33319843349483
1989	54.23032068063268
1990	54.24690779357642
1991	53.6073155018568
1992	53.6149265199857
1993	53.841515586066286
1994	54.95841530590409
1995	55.353956281438684
1996	55.70070465507621
1997	56.43734537742713
1998	56.746076658595975
1999	57.14919758815214
2000	57.281158737860466
2001	56.870042257681476
2002	56.30431311829322
2003	56.26733405180349
2004	56.148033035203945
2005	56.37992843653594
2006	56.76038060380203
2007	56.85178938044653
2008	56.511335153758935
2009	54.780427279482254
2010	54.00314635838367
2011	53.64711963825666
2012	53.6198625968388
2013	53.670744488669605
2014	53.95048739322323
2015	54.13857820893098
2016	54.43607681591827
2017	54.922091520836474
2018	55.216522399344804
2019	55.68273235349676
2020	51.785226307390325
2021	53.52559183774005
2022	55.11837531474572
2023	55.682902903569