Year	per 1,000
1990	18.5
1991	18.2
1992	18
1993	17.8
1994	17.6
1995	17.4
1996	17.2
1997	17
1998	16.8
1999	16.6
2000	16.4
2001	16.1
2002	15.8
2003	15.5
2004	15.1
2005	14.8
2006	14.5
2007	14.2
2008	13.9
2009	13.7
2010	13.5
2011	13.3
2012	13.1
2013	12.9
2014	12.8
2015	12.7
2016	12.5
2017	12.3
2018	12.2
2019	12.1
2020	12
2021	11.8
2022	13.7