Year	Number
1961	15.11764705882353
1962	15.789473684210526
1963	16.374269005847953
1964	17.49271137026239
1965	18.075801749271136
1966	18.6046511627907
1967	19.476744186046513
1968	20.28985507246377
1969	21.44927536231884
1970	22.318840579710145
1971	25.43352601156069
1972	34.68208092485549
1973	44.95677233429395
1974	62.824207492795395
1975	80.45977011494253
1976	85.0574712643678
1977	91.69054441260745
1978	114.28571428571428
1979	128.57142857142858
1980	132.344552196235
1981	141.0693970420933
1982	147.30878186968837
1983	151.54929577464787
1984	151.68539325842696
1985	151.65081141578062
1986	151.53203342618383
1987	151.77777777777777
1988	162.31111111111113
1989	164.5207756232687
1990	184.33240997229916
1991	187.1657458563536
1992	189.98347107438016
1993	193.3168044077135
1994	195.57260273972602
1995	194.10160427807486
1996	181.96252465483235
1997	184.9457593688363
1998	209.98347107438016
1999	217.35537190082647
2000	218.91460055096417