Year	per 1,000
1990	32
1991	31.6
1992	31.3
1993	31.2
1994	31.2
1995	31.2
1996	31.2
1997	31.2
1998	31.2
1999	31.2
2000	31.2
2001	31.2
2002	31.2
2003	31.2
2004	31.2
2005	31.2
2006	31.1
2007	30.9
2008	30.5
2009	30
2010	29.4
2011	28.8
2012	28.2
2013	27.6
2014	27.1
2015	26.6
2016	26.1
2017	25.5
2018	25
2019	24.5
2020	24
2021	23.6
2022	27.3