Year	Number
1997	19.67092
1998	24.69802
1999	25.07315
2000	25.59867
2001	24.16829
2002	22.91954
2003	22.7947
2004	20.80025
2005	19.87007
2006	20.70925
2007	19.92805
2008	20.76451
2009	24.32191
2010	21.04433
2011	21.43269
2012	21.19845
2013	21.36857
2014	21.65238
2015	20.92177
2016	20.65844
2017	20.69471
2018	20.4348