Year	per 1,000
1990	7.8
1991	7.7
1992	7.6
1993	7.6
1994	8.5
1995	7.4
1996	7.3
1997	7.1
1998	6.9
1999	6.8
2000	6.6
2001	6.4
2002	6.3
2003	6.2
2004	6.1
2005	5.9
2006	5.8
2007	5.7
2008	5.6
2009	5.5
2010	5.5
2011	5.4
2012	5.3
2013	5.3
2014	5.2
2015	5.1
2016	5.1
2017	5
2018	4.9
2019	4.7
2020	4.6
2021	4.5
2022	4.5