Year	per 1,000
1990	3
1991	3.1
1992	3.1
1993	3.1
1994	3.1
1995	3.1
1996	3.1
1997	3.1
1998	3.2
1999	3.2
2000	3.1
2001	3.1
2002	3
2003	2.9
2004	2.7
2005	2.6
2006	2.5
2007	2.4
2008	2.3
2009	2.2
2010	2.1
2011	2
2012	1.9
2013	1.9
2014	1.9
2015	1.8
2016	1.8
2017	1.8
2018	1.9
2019	1.9
2020	2
2021	2.1
2022	2.2