Year	per 1,000
1990	0.9
1991	0.9
1992	0.9
1993	0.8
1994	0.8
1995	0.8
1996	0.7
1997	0.7
1998	0.7
1999	0.7
2000	0.7
2001	0.6
2002	0.6
2003	0.6
2004	0.6
2005	0.6
2006	0.5
2007	0.5
2008	0.5
2009	0.5
2010	0.5
2011	0.5
2012	0.5
2013	0.4
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