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