Year	Number
1997	22.75761
2000	22.56784
2001	21.75244
2003	21.49541
2008	19.4078
2009	20.17793
2010	19.70208
2011	19.86917
2012	19.48298
2013	19.12103
2014	18.92294
2015	18.61557
2016	18.19844
2017	17.94478
2018	17.57287