Year	per 1,000
1990	2.2
1991	2.2
1992	2.3
1993	2.3
1994	2.3
1995	2.3
1996	2.4
1997	2.4
1998	2.4
1999	2.4
2000	2.4
2001	2.4
2002	2.4
2003	2.4
2004	2.3
2005	2.3
2006	2.3
2007	2.2
2008	2.2
2009	2.1
2010	2
2011	2
2012	1.9
2013	1.8
2014	1.8
2015	1.7
2016	1.6
2017	1.5
2018	1.5
2019	1.4
2020	1.3
2021	1.3
2022	1.2