Year	per 1,000
1990	5.9
1991	6.4
1992	7.1
1993	7.7
1994	8.4
1995	9.2
1996	9.8
1997	10.4
1998	10.8
1999	11.1
2000	11.1
2001	11.1
2002	11
2003	10.9
2004	10.8
2005	10.6
2006	10.4
2007	10.3
2008	10.1
2009	10
2010	9.9
2011	9.7
2012	9.6
2013	9.5
2014	9.3
2015	9.2
2016	9
2017	8.9
2018	8.7
2019	8.5
2020	8.2
2021	8
2022	7.7