Year	per 1,000
1990	7.1
1991	7
1992	6.8
1993	6.7
1994	6.5
1995	6.4
1996	6.3
1997	6.3
1998	6.2
1999	6.1
2000	6.1
2001	6
2002	6
2003	6
2004	5.9
2005	5.9
2006	5.9
2007	5.9
2008	5.9
2009	5.9
2010	5.9
2011	5.9
2012	5.9
2013	5.9
2014	5.8
2015	5.8
2016	5.8
2017	5.7
2018	5.6
2019	5.6
2020	5.5
2021	5.4
2022	5.3