Year	per 1,000
1990	12.8
1991	12.5
1992	12.1
1993	11.7
1994	11.3
1995	10.9
1996	10.5
1997	10.2
1998	9.8
1999	9.5
2000	9.1
2001	8.8
2002	8.5
2003	8.1
2004	7.8
2005	7.5
2006	7.2
2007	6.9
2008	6.7
2009	6.4
2010	6.2
2011	6
2012	5.9
2013	5.7
2014	5.5
2015	5.4
2016	5.2
2017	5.1
2018	4.9
2019	4.8
2020	4.7
2021	4.5
2022	4.4