Year	per 1,000
1990	26.8
1991	26.2
1992	25.5
1993	24.9
1994	24.3
1995	23.7
1996	23
1997	22.5
1998	21.9
1999	21.3
2000	20.7
2001	20.2
2002	19.6
2003	19.1
2004	18.6
2005	18.1
2006	17.6
2007	17.1
2008	16.6
2009	16
2010	15.6
2011	15.1
2012	14.6
2013	14.1
2014	13.7
2015	13.3
2016	12.8
2017	12.4
2018	12
2019	11.6
2020	11.3
2021	10.9
2022	10.5