Year	Number
1975	19.9102
1976	20.92181
1987	21.47922
1988	16.22646
1991	24.87007
2000	23.8399
2001	24.08889
2002	23.56295
2003	22.02288
2004	18.08348
2007	19.75044
2008	19.46656
2009	13.20993
2010	16.80294
2011	16.81077
2012	15.32206
2013	14.72238
2014	15.43582
2015	15.01606
2016	14.33003
2017	14.36506
2018	13.8727