Year	per 1,000
1990	29.3
1991	26.7
1992	26.6
1993	26.3
1994	25.8
1995	25.1
1996	24.3
1997	23.4
1998	22.4
1999	23.3
2000	20.5
2001	19.5
2002	18.6
2003	17.8
2004	17
2005	16.3
2006	15.5
2007	14.7
2008	14
2009	13.2
2010	12.4
2011	11.7
2012	11
2013	10.4
2014	9.8
2015	9.3
2016	8.8
2017	8.5
2018	8.2
2019	7.9
2020	7.7
2021	7.5
2022	7.3