Year	per 1,000
1990	1.3
1991	1.2
1992	1.1
1993	1
1994	1
1995	0.9
1996	0.8
1997	0.8
1998	0.7
1999	0.6
2000	0.6
2001	0.6
2002	0.5
2003	0.5
2004	0.5
2005	0.4
2006	0.4
2007	0.4
2008	0.4
2009	0.3
2010	0.3
2011	0.3
2012	0.3
2013	0.3
2014	0.3
2015	0.3
2016	0.2
2017	0.2
2018	0.2
2019	0.2
2020	0.2
2021	0.2
2022	0.2