Year	per 1,000
1990	10
1991	9.6
1992	9.3
1993	9
1994	8.7
1995	8.4
1996	8.1
1997	7.9
1998	7.6
1999	7.5
2000	7.3
2001	7.1
2002	7
2003	6.9
2004	6.8
2005	6.8
2006	6.7
2007	6.7
2008	6.8
2009	6.8
2010	7
2011	7
2012	7.2
2013	7.1
2014	7
2015	6.8
2016	6.7
2017	6.5
2018	6.3
2019	6.1
2020	6
2021	5.8
2022	5.6