Year	per 1,000
1990	7.1
1991	7.5
1992	7.7
1993	7.8
1994	7.9
1995	7.9
1996	8
1997	8.2
1998	8.4
1999	8.6
2000	8.7
2001	8.5
2002	8.1
2003	7.7
2004	7.4
2005	7.2
2006	6.8
2007	6.5
2008	6.2
2009	6
2010	5.8
2011	5.4
2012	5
2013	4.6
2014	4.1
2015	3.7
2016	3.3
2017	3
2018	2.7
2019	2.5
2020	2.4
2021	2.3
2022	2.2