Year	per 1,000
1990	12.9
1991	13
1992	13.1
1993	13.2
1994	13.4
1995	13.6
1996	13.7
1997	13.9
1998	14
1999	14.1
2000	14.1
2001	14.1
2002	13.9
2003	13.7
2004	13.5
2005	13.3
2006	13
2007	12.8
2008	12.5
2009	12.3
2010	12.1
2011	12
2012	11.8
2013	11.6
2014	11.5
2015	11.3
2016	11.1
2017	10.9
2018	10.6
2019	10.3
2020	10
2021	9.8
2022	9.4