Year	Number
1998	17.34478
1999	24.18968
2000	22.2584
2001	21.01976
2002	19.84569
2003	21.59308
2004	22.86816
2005	21.84844
2006	24.19409
2007	21.70775
2008	24.43188
2009	26.60483
2011	37.83382
2012	32.55726
2013	30.9129
2014	31.1
2015	23.49557
2017	22.4713
2018	19.33544