Year	per 1,000
1990	19.4
1991	19.3
1992	19.3
1993	19.3
1994	19.4
1995	19.7
1996	19.9
1997	20.2
1998	20.6
1999	20.8
2000	21.1
2001	21.3
2002	21.5
2003	21.6
2004	21.8
2005	22
2006	22.3
2007	22.5
2008	22.7
2009	23
2010	23.3
2011	23.4
2012	23.4
2013	23.2
2014	23.1
2015	22.9
2016	22.6
2017	22.3
2018	22.1
2019	21.8
2020	21.6
2021	21.2
2022	21