Year	per 1,000
1990	2.4
1991	2.3
1992	2.3
1993	2.3
1994	2.2
1995	3.7
1996	2.2
1997	2.2
1998	2.1
1999	2.1
2000	2
2001	2
2002	2
2003	1.9
2004	1.9
2005	1.8
2006	1.8
2007	1.7
2008	1.6
2009	1.6
2010	1.5
2011	1.4
2012	1.4
2013	1.3
2014	1.2
2015	1.2
2016	1.2
2017	1.1
2018	1.1
2019	1
2020	1
2021	1
2022	1