Year	per 1,000
1990	9.1
1991	8.9
1992	8.7
1993	8.6
1994	8.4
1995	8.2
1996	8.1
1997	7.9
1998	7.8
1999	7.6
2000	7.5
2001	7.3
2002	7.2
2003	7
2004	6.9
2005	6.8
2006	6.6
2007	6.5
2008	6.3
2009	6.2
2010	6
2011	5.9
2012	5.8
2013	5.6
2014	5.5
2015	5.3
2016	5.2
2017	5.1
2018	4.9
2019	4.8
2020	4.6
2021	4.5
2022	4.4