Year	per 1,000
1990	17.5
1991	17.2
1992	17.1
1993	17.3
1994	25.5
1995	16.7
1996	16.6
1997	16.2
1998	15.9
1999	15.7
2000	15.1
2001	14.7
2002	14.4
2003	14
2004	13.7
2005	13.3
2006	13
2007	12.6
2008	12.4
2009	12
2010	11.7
2011	11.5
2012	11.3
2013	11.1
2014	10.9
2015	10.7
2016	10.5
2017	10.2
2018	10
2019	9.8
2020	9.6
2021	9.3
2022	9.2