Year	per 1,000
1990	10
1991	10
1992	10
1993	10
1994	10
1995	10
1996	10
1997	9.9
1998	9.9
1999	9.9
2000	9.9
2001	9.9
2002	9.9
2003	9.9
2004	9.9
2005	9.9
2006	9.9
2007	9.9
2008	9.9
2009	9.9
2010	9.8
2011	9.8
2012	9.8
2013	9.8
2014	9.7
2015	9.7
2016	9.6
2017	9.5
2018	9.4
2019	9.2
2020	9.1
2021	8.9
2022	8.7