Year	per 1,000
1990	15.2
1991	14.7
1992	14.5
1993	14.1
1994	13.8
1995	13.5
1996	13.3
1997	13.1
1998	12.8
1999	12.6
2000	12.4
2001	12.3
2002	12.2
2003	12
2004	12
2005	12
2006	12
2007	12.1
2008	12.2
2009	12.4
2010	12.6
2011	12.8
2012	13.1
2013	13.2
2014	13.1
2015	13
2016	12.9
2017	12.8
2018	12.6
2019	12.5
2020	12.3
2021	12.2
2022	12