Year	per 1,000
1990	10.4
1991	10.2
1992	9.8
1993	9.6
1994	9.4
1995	9.2
1996	8.9
1997	8.7
1998	8.5
1999	8.2
2000	8
2001	7.8
2002	7.7
2003	7.5
2004	7.4
2005	7.3
2006	7.1
2007	6.9
2008	6.9
2009	6.6
2010	6.5
2011	6.2
2012	6
2013	5.9
2014	5.7
2015	5.6
2016	5.4
2017	5.3
2018	5.1
2019	4.9
2020	4.8
2021	4.6
2022	4.5