Year	per 1,000
1990	3.6
1991	5.5
1992	4.4
1993	4.3
1994	4
1995	3.6
1996	3.2
1997	3
1998	2.8
1999	2.7
2000	2.7
2001	2.6
2002	2.6
2003	2.5
2004	2.5
2005	2.4
2006	2.3
2007	2.3
2008	2.1
2009	2
2010	1.9
2011	1.7
2012	1.6
2013	1.6
2014	1.5
2015	1.5
2016	1.5
2017	1.6
2018	1.7
2019	1.8
2020	1.9
2021	2
2022	2.1