Year	per 1,000
1990	1.8
1991	1.8
1992	1.7
1993	1.7
1994	1.6
1995	1.6
1996	1.6
1997	1.6
1998	1.6
1999	1.5
2000	1.5
2001	1.5
2002	1.5
2003	1.5
2004	1.5
2005	1.5
2006	1.5
2007	1.5
2008	1.5
2009	1.5
2010	1.4
2011	1.4
2012	1.3
2013	1.3
2014	1.2
2015	1.2
2016	1.2
2017	1.1
2018	1.1
2019	1.1
2020	1
2021	1
2022	1