Year	Number
1971	9.77862
1973	9.69272
1976	10.01925
1977	10.94819
1978	10.92963
1979	10.78786
1980	10.28345
1981	10.19155
1982	8.63537
1983	8.76944
1984	8.94866
1985	10.87986
1986	10.63812
1987	11.70514
1988	11.31738
1989	11.99906
1990	14.16992
1991	14.9959
1997	13.56165
1998	13.20724
1999	13.29
2000	13.06755
2001	12.26234
2012	10.0827
2013	10.45972
2014	10.29124
2015	9.9275
2016	9.42312
2017	8.56173