Year	per 1,000
1990	2
1991	2
1992	1.9
1993	1.9
1994	1.8
1995	1.8
1996	1.8
1997	1.7
1998	1.7
1999	1.7
2000	1.7
2001	1.7
2002	1.7
2003	1.6
2004	1.6
2005	1.6
2006	1.6
2007	1.6
2008	1.6
2009	1.6
2010	1.6
2011	1.6
2012	1.6
2013	1.6
2014	1.6
2015	1.6
2016	1.6
2017	1.6
2018	1.5
2019	1.5
2020	1.5
2021	1.5
2022	1.5