Year	Number
1971	9.40152
1972	11.26051
1974	11.60328
1975	11.19329
1976	12.36468
1977	10.53021
1978	9.97281
1979	10.21927
1985	11.83951
1986	12.49328
1987	13.94238
1988	15.0599
1989	15.85902
1999	15.92951
2006	14.06245
2007	14.06232
2008	15.35098
2009	16.42257
2011	21.09729
2013	15.3402