Year	per 1,000
1990	4.9
1991	4.9
1992	4.7
1993	4.4
1994	4.1
1995	3.8
1996	3.5
1997	3.4
1998	3.3
1999	3.2
2000	3.1
2001	3
2002	2.9
2003	2.9
2004	2.8
2005	2.7
2006	2.7
2007	2.6
2008	2.5
2009	2.4
2010	2.3
2011	2.2
2012	2.1
2013	2.1
2014	2
2015	2
2016	2
2017	2
2018	2
2019	2.1
2020	2.1
2021	2.2
2022	2.2