Year	per 1,000
1990	16.3
1991	16.4
1992	16.6
1993	16.9
1994	17.2
1995	17.6
1996	17.9
1997	18.3
1998	18.7
1999	19.1
2000	19.4
2001	19.7
2002	19.8
2003	19.7
2004	19.5
2005	19.1
2006	18.7
2007	18.2
2008	17.8
2009	17.3
2010	16.9
2011	16.5
2012	16.1
2013	15.8
2014	15.6
2015	15.3
2016	15.1
2017	14.9
2018	14.8
2019	14.5
2020	14.3
2021	14.1
2022	14