Year	per 1,000
1990	22.7
1991	23.8
1992	25.1
1993	26.4
1994	27.7
1995	29.1
1996	30.2
1997	30.9
1998	31.2
1999	30.9
2000	30.2
2001	29
2002	27.7
2003	26.3
2004	24.8
2005	23.5
2006	22.2
2007	21.1
2008	20
2009	19
2010	18.1
2011	17.2
2012	16.3
2013	15.5
2014	14.6
2015	13.9
2016	13.2
2017	12.7
2018	12.1
2019	11.7
2020	11.4
2021	11.2
2022	11