Year	per 1,000
1990	3.4
1991	3.1
1992	2.9
1993	2.7
1994	2.5
1995	2.3
1996	2.2
1997	2
1998	1.9
1999	1.8
2000	1.7
2001	1.6
2002	1.6
2003	1.5
2004	1.5
2005	1.4
2006	1.4
2007	1.6
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	1.3
2018	1.2
2019	1.2
2020	1.2
2021	1.2
2022	1.2