Year	Number
1977	25.19845
1978	25.45616
1981	22.40541
1982	20.07692
1983	20.30737
1984	18.47461
1985	18.7865
1987	19.38428
1988	17.85903
1989	16.50764
1990	15.34045
1991	17.1426
1992	16.60403
1993	16.44732
1994	17.11718
1995	17.93824
2011	10.38663
2012	9.61612
2013	9.99168
2014	9.85905
2015	9.86281
2016	9.79181
2017	10.1467
2018	10.23948