Year	per 1,000
1990	12.8
1991	12.4
1992	11.9
1993	11.5
1994	11.1
1995	10.7
1996	10.3
1997	9.8
1998	9.5
1999	9.1
2000	8.7
2001	8.3
2002	8
2003	7.6
2004	7.3
2005	7
2006	7.6
2007	6.5
2008	6.2
2009	5.9
2010	5.7
2011	5.5
2012	5.3
2013	5.2
2014	5
2015	4.9
2016	4.7
2017	4.6
2018	4.4
2019	4.3
2020	4.1
2021	4
2022	3.9