Year	Number
1961	18.34857142857143
1962	18.337142857142858
1963	17.46
1964	16.52285714285714
1965	16.36857142857143
1966	17.557142857142857
1967	18.905714285714286
1968	14.011428571428572
1969	17.137142857142855
1970	20.705714285714286
1971	16.83142857142857
1972	17.222857142857144
1973	16.345714285714287
1974	17.7
1975	15.823684210526315
1976	15.742105263157894
1977	16.278947368421054
1978	16.97105263157895
1979	16.773684210526316
1980	17.226315789473684
1981	16.839473684210525
1982	17.5
1983	22.54736842105263
1984	23.624161073825505
1985	19.676432006996063
1986	20.03048116699325
1987	20.193340494092375
1988	19.664072101597707
1989	18.585245590745306
1990	20.04008016032064
1991	20.011771630370806
1992	19.841269841269842
1993	21.34387351778656
1994	20.176082171680118
1995	20.595807282089005
1996	24.405908798972384
1997	24.096385542168676
1998	25.224454895254382
1999	23.547880690737834
2000	24.94377427928849
2001	24.50858034321373
2002	25.228835199371442