Year	Number
1971	14.51252
1972	14.55993
1975	15.05522
1976	14.88439
1977	14.88393
1978	14.7063
1979	14.4916
1980	14.51397
1982	14.39342
1983	14.31168
1984	14.57236
1985	14.56727
1986	16.59932
1987	16.09469
1988	15.60104
1989	15.30169
1990	15.54023
1991	15.68467
1992	15.80009
1993	15.9245
1994	17.41098
2002	13.46918
2003	13.08537
2004	12.73649
2005	13.13236
2006	13.30748
2007	13.31665
2008	13.18227
2009	13.39986
2010	13.72933
2011	13.57412
2012	13.85693
2015	14.46276
2016	14.40346
2017	14.51694