Year	per 1,000
1990	29.1
1991	28.4
1992	27.6
1993	27.3
1994	29.6
1995	24.9
1996	23.9
1997	23
1998	22
1999	20.9
2000	19.8
2001	18.9
2002	18
2003	17
2004	16.1
2005	15.4
2006	14.6
2007	13.9
2008	13.3
2009	12.6
2010	12.1
2011	11.6
2012	11.3
2013	10.9
2014	10.4
2015	10.1
2016	9.7
2017	9.4
2018	9.3
2019	8.9
2020	8.7
2021	8.5
2022	8.3