Year	per 1,000
1990	17.3
1991	16.6
1992	15.9
1993	15.1
1994	14.2
1995	13.3
1996	12.4
1997	11.4
1998	10.4
1999	9.4
2000	8.6
2001	7.8
2002	7.1
2003	6.6
2004	6.1
2005	5.8
2006	5.5
2007	5.4
2008	5.2
2009	5.1
2010	5.1
2011	5
2012	4.9
2013	4.9
2014	4.9
2015	5
2016	5
2017	5.1
2018	5.2
2019	5.2
2020	5.3
2021	5.3
2022	5.2