Year	per 1,000
1990	8
1991	8.7
1992	9.3
1993	9.7
1994	9.8
1995	9.5
1996	9
1997	8.5
1998	8.1
1999	7.7
2000	7.6
2001	7.5
2002	7.4
2003	7.3
2004	7.1
2005	6.9
2006	6.6
2007	6.2
2008	5.8
2009	5.3
2010	4.8
2011	4.4
2012	4.1
2013	3.7
2014	3.4
2015	3.2
2016	2.9
2017	2.7
2018	2.4
2019	2.2
2020	2
2021	1.8
2022	1.7