Year	Number
1971	27.0482
2004	27.03779
2005	26.43142
2007	29.02851
2008	24.46806
2009	26.94102
2010	28.19246
2011	28.72223
2012	29.17577
2013	27.63296
2015	22.09344
2017	18.64652