Year	per 1,000
1990	3
1991	3
1992	3.1
1993	3.1
1994	3.1
1995	3.1
1996	3.1
1997	3.1
1998	3.1
1999	3.1
2000	3
2001	2.9
2002	2.9
2003	2.8
2004	2.7
2005	2.7
2006	2.6
2007	2.6
2008	2.5
2009	2.5
2010	2.5
2011	2.6
2012	2.6
2013	2.6
2014	2.6
2015	2.5
2016	2.5
2017	2.5
2018	2.6
2019	2.6
2020	2.6
2021	2.6
2022	2.5