Year	Number
1974	23.39695
1976	20.42576
1977	20.02584
1978	19.78972
1979	20.26566
1981	23.41024
1982	22.57271
1983	22.86187
1984	20.2595
1985	19.80331
1989	17.16543
1990	19.61111
1999	17.75691
2000	17.29712
2001	17.24463
2002	15.74057
2003	15.16799
2004	16.85127
2005	15.88872
2006	14.58392
2015	17.53754
2016	18.63678
2017	18.45852
2018	17.93859