Year	per 1,000
1990	12.1
1991	12
1992	11.8
1993	12.2
1994	16.7
1995	11.2
1996	10.9
1997	10.7
1998	10.5
1999	10.1
2000	9.8
2001	9.5
2002	9.2
2003	8.8
2004	8.5
2005	8.2
2006	8
2007	7.7
2008	7.6
2009	7.3
2010	7.2
2011	7
2012	6.9
2013	6.7
2014	6.6
2015	6.4
2016	6.3
2017	6.2
2018	6.1
2019	6
2020	5.9
2021	5.8
2022	5.8