Year	% of total labor force (national estimate)
1991	0.05
1992	0.5
1993	1.4
1994	2.1
1995	2.9
1996	4
1997	2.8
1998	2.3
1999	2.1
2000	2.1
2001	2.3
2002	3
2003	3.1
2004	1.9
2005	1.5
2006	1.2
2007	1
2008	0.8
2009	6.1
2011	0.6
2012	0.5
2013	0.5
2014	0.5
2015	1
2016	5.844
2017	5.648
2018	4.763
2019	4.165
2020	4.049
2021	3.9
2022	3.574