Year	per 1,000
1990	1.4
1991	1.3
1992	1.2
1993	1.1
1994	1
1995	1
1996	0.9
1997	0.8
1998	0.8
1999	0.7
2000	0.7
2001	0.6
2002	0.6
2003	0.6
2004	0.5
2005	0.5
2006	0.5
2007	0.5
2008	0.4
2009	0.4
2010	0.4
2011	0.4
2012	0.4
2013	0.3
2014	0.3
2015	0.3
2016	0.3
2017	0.3
2018	0.3
2019	0.3
2020	0.3
2021	0.3
2022	0.2