Year	per 1,000
1990	2.3
1991	2.2
1992	2.2
1993	2.2
1994	2.1
1995	2.1
1996	2.1
1997	2
1998	2
1999	2
2000	2
2001	1.9
2002	1.9
2003	1.9
2004	1.9
2005	1.9
2006	1.9
2007	1.9
2008	1.9
2009	1.9
2010	1.9
2011	1.8
2012	1.8
2013	1.8
2014	1.8
2015	1.7
2016	1.7
2017	5.2
2018	1.6
2019	1.6
2020	1.5
2021	1.5
2022	1.4