Year	per 1,000
1990	10.8
1991	10.5
1992	10.3
1993	10
1994	9.7
1995	9.5
1996	9.2
1997	9
1998	8.7
1999	8.5
2000	8.2
2001	8
2002	7.7
2003	7.5
2004	7.3
2005	7.1
2006	7
2007	6.8
2008	6.6
2009	6.5
2010	6.3
2011	6.2
2012	6
2013	5.9
2014	5.8
2015	5.6
2016	5.5
2017	5.4
2018	5.3
2019	5.2
2020	5
2021	4.9
2022	4.8