Year	per 1,000
1990	2.2
1991	2.2
1992	2.2
1993	2.2
1994	2.1
1995	2.1
1996	2.1
1997	2.1
1998	2
1999	2
2000	2
2001	1.9
2002	1.9
2003	1.9
2004	1.9
2005	1.9
2006	1.9
2007	1.9
2008	1.9
2009	1.9
2010	1.9
2011	1.9
2012	1.9
2013	1.9
2014	1.8
2015	1.8
2016	1.8
2017	1.8
2018	1.7
2019	1.7
2020	1.7
2021	1.7
2022	1.7