Year	per 1,000
1990	6.8
1991	6.7
1992	6.6
1993	6.5
1994	6.4
1995	6.3
1996	6.2
1997	6.1
1998	6
1999	5.9
2000	5.9
2001	5.8
2002	5.7
2003	5.6
2004	5.6
2005	5.5
2006	5.4
2007	5.3
2008	5.3
2009	5.2
2010	5.1
2011	5
2012	5
2013	4.9
2014	4.8
2015	4.7
2016	4.6
2017	4.6
2018	4.5
2019	4.4
2020	4.3
2021	4.2
2022	4.2