Year	per 1,000
1990	22
1991	21.7
1992	21.4
1993	21
1994	20.7
1995	20.4
1996	20
1997	19.7
1998	23.2
1999	21.6
2000	18.6
2001	18.2
2002	17.8
2003	17.4
2004	16.9
2005	16.5
2006	16
2007	15.5
2008	15
2009	14.6
2010	14.1
2011	13.6
2012	13.2
2013	12.8
2014	12.5
2015	12.2
2016	11.9
2017	11.6
2018	11.3
2019	11.1
2020	10.8
2021	10.6
2022	10.3