Year	per 1,000
1990	2
1991	2
1992	1.9
1993	1.9
1994	1.9
1995	1.9
1996	1.9
1997	1.9
1998	1.8
1999	1.8
2000	1.8
2001	1.7
2002	1.6
2003	1.6
2004	1.5
2005	1.4
2006	1.3
2007	1.2
2008	1.2
2009	1.2
2010	1.1
2011	1.1
2012	1
2013	1
2014	1
2015	1
2016	1
2017	1
2018	1
2019	1
2020	1
2021	1
2022	1.1