Year	per 1,000
1990	4.2
1991	3.8
1992	3.5
1993	3.2
1994	2.9
1995	2.7
1996	2.4
1997	2.3
1998	2.1
1999	2
2000	1.8
2001	1.7
2002	1.6
2003	1.5
2004	1.5
2005	1.4
2006	1.4
2007	1.5
2008	1.4
2009	1.3
2010	1.3
2011	1.3
2012	1.3
2013	1.3
2014	1.3
2015	1.3
2016	1.3
2017	1.2
2018	1.2
2019	1.2
2020	1.2
2021	1.2
2022	1.1