Year	per 1,000
1990	3
1991	3
1992	3
1993	3
1994	3
1995	2.9
1996	2.8
1997	2.7
1998	2.6
1999	2.6
2000	2.5
2001	2.4
2002	2.4
2003	2.4
2004	2.3
2005	2.3
2006	2.3
2007	2.2
2008	2.1
2009	2
2010	1.9
2011	1.8
2012	1.7
2013	1.6
2014	1.5
2015	1.5
2016	1.4
2017	1.4
2018	1.3
2019	1.3
2020	1.3
2021	1.2
2022	1.2