Year	per 1,000
1990	16.4
1991	16.4
1992	16.4
1993	16.4
1994	16.4
1995	16.4
1996	16.4
1997	16.5
1998	16.5
1999	16.5
2000	16.6
2001	16.5
2002	16.4
2003	16.3
2004	16.1
2005	15.9
2006	15.7
2007	15.5
2008	15.3
2009	15.1
2010	14.9
2011	14.6
2012	14.3
2013	14.1
2014	13.8
2015	13.5
2016	13.3
2017	13
2018	12.8
2019	12.5
2020	12.3
2021	12.1
2022	11.9