Year	per 1,000
1990	8.5
1991	9
1992	9.6
1993	10.3
1994	11
1995	11.5
1996	11.9
1997	12
1998	11.9
1999	11.7
2000	11.4
2001	11.1
2002	11
2003	10.9
2004	11
2005	11
2006	10.8
2007	10.2
2008	9.4
2009	8.5
2010	7.7
2011	7
2012	6.4
2013	5.9
2014	5.4
2015	5
2016	4.7
2017	4.6
2018	4.4
2019	4.3
2020	4.2
2021	4.1
2022	4