Year	Number
1971	15.52916
1974	23.20236
1977	26.90567
1978	23.42989
1984	18.73195
1985	18.99799
1987	17.55675
1988	17.12475
1989	16.25751
1990	16.22193
1991	16.65947
1992	18.22766
1993	19.18826
1994	20.15833
2001	24.03813
2002	23.99672
2006	21.69429
2007	21.01242
2008	21.22434
2014	29.53685
2015	28.15431
2016	26.63435
2017	26.36914
2018	25.94603