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