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