Year	per 1,000
1990	6.3
1991	3.3
1992	3.1
1993	3
1994	2.8
1995	2.7
1996	2.6
1997	2.5
1998	2.5
1999	2.4
2000	2.4
2001	2.4
2002	2.4
2003	4.1
2004	2.5
2005	2.5
2006	2.6
2007	2.7
2008	2.7
2009	2.8
2010	2.7
2011	2.6
2012	2.5
2013	2.4
2014	2.2
2015	2.1
2016	2
2017	1.9
2018	1.8
2019	1.7
2020	1.7
2021	1.6
2022	1.6