Year	per 1,000
1990	44.8
1991	45.8
1992	46.7
1993	80.7
1994	47.2
1995	46.4
1996	44.6
1997	41.9
1998	38.6
1999	35.2
2000	31.6
2001	28.3
2002	25.3
2003	22.8
2004	20.5
2005	18.3
2006	16.4
2007	14.7
2008	13.3
2009	12.2
2010	11.5
2011	11
2012	10.6
2013	10.2
2014	10
2015	9.7
2016	9.5
2017	9.3
2018	9.1
2019	9.1
2020	9
2021	8.9
2022	8.8