Year	per 1,000
1990	23.5
1991	22.4
1992	21.3
1993	20.3
1994	19.5
1995	18.7
1996	18.1
1997	17.5
1998	17
1999	16.4
2000	15.9
2001	15.4
2002	14.8
2003	14.3
2004	13.7
2005	13.3
2006	12.8
2007	12.3
2008	11.9
2009	11.5
2010	11.2
2011	10.9
2012	10.7
2013	10.6
2014	10.6
2015	10.6
2016	10.8
2017	11
2018	11.3
2019	11.6
2020	11.9
2021	12
2022	12.1