Year	Number
1999	26.49727
2000	29.03651
2001	27.52506
2002	25.74874
2003	27.10889
2004	28.20523
2005	26.62175
2006	29.39718
2007	26.38583
2008	25.17536
2009	24.28426
2010	23.16124
2011	21.13986
2012	20.92793
2013	20.67567
2014	20.679
2015	21.30407
2016	21.20244
2017	21.61808
2018	18.60687