Year	per 1,000
1990	3
1991	2.7
1992	2.5
1993	2.3
1994	2.2
1995	2
1996	1.9
1997	1.8
1998	2.3
1999	1.6
2000	1.6
2001	2.4
2002	1.5
2003	1.4
2004	1.4
2005	1.4
2006	1.3
2007	1.3
2008	1.3
2009	1.6
2010	1.2
2011	1.2
2012	1.2
2013	1.2
2014	1.2
2015	1.2
2016	1.2
2017	1.2
2018	1.2
2019	1.3
2020	1.3
2021	1.3
2022	1.2