Year	per 1,000
1990	9.3
1991	8.8
1992	8.3
1993	7.9
1994	7.6
1995	7.3
1996	7
1997	6.8
1998	6.5
1999	6.3
2000	6.2
2001	6
2002	5.9
2003	5.8
2004	5.7
2005	5.6
2006	5.6
2007	5.6
2008	5.6
2009	5.7
2010	5.8
2011	5.9
2012	6
2013	6.1
2014	6.2
2015	6.4
2016	6.5
2017	6.7
2018	6.8
2019	6.9
2020	6.9
2021	6.8
2022	6.7