Year	per 1,000
1990	19.5
1991	18.9
1992	18.8
1993	19.3
1994	34
1995	18.6
1996	18.5
1997	17.9
1998	17.4
1999	17.2
2000	16.2
2001	15.7
2002	15.2
2003	14.5
2004	14
2005	13.6
2006	13.3
2007	12.9
2008	12.7
2009	12.4
2010	12.2
2011	12.1
2012	12.4
2013	12.3
2014	12.1
2015	12.2
2016	11.8
2017	11.6
2018	11.4
2019	10.9
2020	10.6
2021	10.3
2022	10.1