Year	per 1,000
1990	14.4
1991	15
1992	15.6
1993	16.2
1994	16.7
1995	17.2
1996	17.5
1997	17.8
1998	17.9
1999	17.8
2000	17.7
2001	17.5
2002	17.1
2003	16.7
2004	16.3
2005	15.8
2006	15.2
2007	14.6
2008	14.1
2009	13.5
2010	12.9
2011	12.3
2012	11.8
2013	11.3
2014	10.9
2015	10.6
2016	10.4
2017	10.2
2018	10.1
2019	9.9
2020	9.8
2021	9.7
2022	9.6