Year	per 1,000
1990	14.2
1991	14.4
1992	14.6
1993	14.7
1994	14.7
1995	14.6
1996	14.5
1997	14.3
1998	14
1999	13.8
2000	13.4
2001	13.1
2002	12.8
2003	12.4
2004	11.9
2005	11.4
2006	10.9
2007	10.4
2008	9.9
2009	9.4
2010	8.9
2011	8.3
2012	7.9
2013	7.4
2014	7
2015	6.7
2016	6.5
2017	6.4
2018	6.3
2019	6.2
2020	6.1
2021	6.1
2022	6