Year	Number
1997	20.31425
1998	22.23089
1999	23.81978
2000	21.95419
2002	26.84577
2003	23.76007
2004	20.67226
2005	22.15464
2006	25.83207
2007	21.62744
2008	24.20135
2009	23.63875
2010	23.55565
2011	23.58146
2012	25.13758
2013	23.39422
2014	21.41289
2015	17.93859
2016	18.91434
2017	19.47085
2018	18.88925