Year	Number
1972	22.60947
1973	21.79845
1974	19.46897
1975	18.39333
1976	17.77215
1977	17.84667
1978	17.25466
1979	18.61905
1980	18.13423
1981	17.51592
1982	16.92857
1984	16.57627
1985	15.46448
1997	15.86628
1999	28.33696
2000	22.53333
2001	20.66957
2008	16.63731
2009	16.03448
2016	13.70588
2017	14.17