Year	Number
1971	20.392
1972	20.06948
1973	21.42923
1975	29.3806
1976	19.44453
1977	20.32919
1978	19.78284
1984	20.51018
1985	20.51066
1986	31.50931
1988	19.37921
1989	19.49825
1990	18.6619
1991	17.1677
2001	26.63818
2011	20.51483
2012	21.68596
2013	20.66285
2015	20.54128
2016	22.04465