Year	per 1,000
1990	19.6
1991	20.7
1992	21.7
1993	48
1994	23
1995	23.3
1996	23.3
1997	23.2
1998	22.9
1999	22.5
2000	21.6
2001	20.6
2002	19.2
2003	17.6
2004	16
2005	14.4
2006	12.9
2007	11.7
2008	10.7
2009	10
2010	9.5
2011	9.2
2012	9
2013	8.9
2014	8.9
2015	8.8
2016	8.8
2017	8.7
2018	8.6
2019	8.5
2020	8.3
2021	8.2
2022	8