Year	% of total labor force (national estimate)
1970	4.8
1971	6
1972	6.6
1973	5.6
1974	3.4
1975	2.3
1976	4.5
1977	2.8
1978	2.8
1979	2
1980	2.3
1981	4.5
1982	4.73
1983	4.17
1984	3.54
1985	5.3
1986	4.4
1987	5.3
1988	6
1989	7.3
1990	7.06
1991	5.44
1992	6.36
1993	10.1
1994	11.76
1995	18.8
1996	17.11
1997	14.82
1998	12.65
1999	14.05
2000	15
2001	17.32
2002	19.59
2003	15.36
2004	13.522
2005	11.506
2006	10.078
2007	8.47
2008	7.837
2009	8.645
2010	7.714
2011	7.18
2012	7.217
2013	7.1
2014	7.268
2017	8.347
2018	9.221
2019	9.843
2020	11.461
2021	8.736
2022	6.805
2023	6.139