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