Year	Number
1997	28.49039
1998	28.9828
1999	29.86814
2000	29.69827
2001	30.47743
2002	30.33523
2003	29.35098
2004	29.391
2005	28.26413
2006	28.48219
2007	28.48703
2008	28.96008
2009	26.01644
2010	28.15746
2011	28.41682
2012	29.06116
2013	28.61279
2014	28.26937
2015	27.72893
2016	27.73503
2017	26.82036
2018	27.95508