Year	per 1,000
1990	7
1991	6.9
1992	6.9
1993	6.8
1994	6.7
1995	6.6
1996	6.6
1997	6.5
1998	6.4
1999	6.3
2000	6.2
2001	6.1
2002	6
2003	6
2004	6
2005	5.9
2006	5.9
2007	5.9
2008	5.9
2009	5.9
2010	5.8
2011	5.7
2012	5.7
2013	5.6
2014	5.5
2015	5.4
2016	5.3
2017	5.2
2018	5.1
2019	5
2020	4.9
2021	4.8
2022	4.8