Year	per 1,000
1990	17.8
1991	17.6
1992	17.5
1993	17.5
1994	17.4
1995	17.4
1996	17.5
1997	17.7
1998	17.9
1999	18.1
2000	18.2
2001	18.3
2002	18.2
2003	18
2004	17.8
2005	17.5
2006	17.2
2007	16.9
2008	16.7
2009	16.4
2010	16.2
2011	15.9
2012	15.7
2013	15.6
2014	15.4
2015	15.1
2016	14.7
2017	14.4
2018	14.1
2019	13.7
2020	13.3
2021	13
2022	12.6