Year	per 1,000
1990	16.7
1991	16.2
1992	15.7
1993	15.2
1994	14.7
1995	14.2
1996	13.8
1997	13.3
1998	12.9
1999	12.5
2000	12
2001	11.6
2002	11.2
2003	10.8
2004	10.3
2005	10
2006	9.6
2007	9.2
2008	8.9
2009	8.5
2010	8.2
2011	7.9
2012	7.6
2013	7.4
2014	7.1
2015	6.9
2016	6.7
2017	6.4
2018	6.2
2019	6
2020	5.8
2021	5.6
2022	5.4