Year	per 1,000
1990	3
1991	2.8
1992	2.7
1993	2.5
1994	2.4
1995	2.3
1996	2.3
1997	2.3
1998	2.4
1999	2.4
2000	2.5
2001	2.5
2002	2.6
2003	2.6
2004	2.6
2005	2.5
2006	2.5
2007	2.4
2008	2.4
2009	2.3
2010	2.3
2011	2.2
2012	2.2
2013	2.2
2014	2.1
2015	2.1
2016	2.1
2017	2.2
2018	2.2
2019	2.2
2020	2.2
2021	2.1
2022	2.1