Year	Number
1961	10.046367851622875
1962	10.802469135802468
1963	11.503067484662576
1964	11.931394481730052
1965	12.363636363636363
1966	12.729844413012732
1967	13.121546961325967
1968	13.440860215053762
1969	13.7524557956778
1970	14.066496163682865
1971	14.456316781898176
1972	14.687882496940025
1973	15.494636471990464
1974	16.36469900642899
1975	17.123287671232877
1976	17.70890979524073
1977	18.428184281842817
1978	19.17954182205647
1979	19.895287958115183
1980	20.58672156459084
1981	21.21212121212121
1982	21.80376610505451
1983	21.940516821062896
1984	21.978021978021978
1985	23.170731707317074
1986	23.78640776699029
1987	24.154589371980677
1988	24.519230769230766
1989	24.401913875598087
1990	24.761904761904763
1991	25.118483412322274
1992	24.88372093023256
1993	24.31818181818182
1994	22.76595744680851
1995	21.153846153846153
1996	20.817843866171003
1997	19.846796657381617
1998	19.166106254203093
1999	18.566775244299674
2000	19.083969465648856