Year	per 1,000
1990	14.2
1991	13.9
1992	13.3
1993	12.9
1994	12.5
1995	12.2
1996	11.9
1997	11.7
1998	11.5
1999	11.3
2000	11.1
2001	10.8
2002	10.6
2003	10.2
2004	10
2005	9.8
2006	9.3
2007	9
2008	8.7
2009	8.4
2010	8.2
2011	7.9
2012	7.6
2013	7.3
2014	7
2015	6.7
2016	6.4
2017	6.1
2018	5.9
2019	5.7
2020	5.5
2021	5.4
2022	5.3