Year	per 1,000
1990	2.9
1991	3
1992	3
1993	3
1994	2.9
1995	2.8
1996	2.7
1997	2.6
1998	2.5
1999	2.5
2000	2.4
2001	2.4
2002	2.3
2003	2.3
2004	2.2
2005	2.1
2006	2
2007	2
2008	1.9
2009	1.9
2010	1.8
2011	1.8
2012	1.7
2013	1.6
2014	1.6
2015	1.6
2016	1.5
2017	1.5
2018	1.5
2019	1.4
2020	1.4
2021	1.4
2022	1.4