Year	per 1,000
1990	1.3
1991	1.2
1992	1.2
1993	1.2
1994	1.1
1995	1.1
1996	1
1997	1
1998	0.9
1999	0.9
2000	0.8
2001	0.8
2002	0.8
2003	0.7
2004	0.7
2005	0.6
2006	0.6
2007	0.6
2008	0.6
2009	0.5
2010	0.5
2011	0.5
2012	0.5
2013	0.5
2014	0.4
2015	0.4
2016	0.4
2017	0.4
2018	0.4
2019	0.4
2020	0.4
2021	0.4
2022	0.4