Year	Number
1961	16.471375962504183
1962	17.589467284429443
1963	18.613527984606375
1964	19.860440931780367
1965	21.0348957257898
1966	22.757561926891
1967	25.864955357142858
1968	26.964641434262948
1969	28.389367340178868
1970	29.519270446480153
1971	29.944566740044028
1972	31.860701677403913
1973	34.72206360145712
1974	37.85645062399873
1975	41.63346214684741
1976	44.53143511174474
1977	47.36041331895938
1978	52.60883898217781
1979	56.69907632474477
1980	63.36647364387294
1981	67.6255271743455
1982	71.50468306424324
1983	77.95781341336475
1984	84.43478874881562
1985	93.45339424148531
1986	100.03973257544122
1987	104.4709945583422
1988	107.98833293240318
1989	109.40125838858589
1990	115.74983114627557
1991	115.52264323178562
1992	115.21736077184967
1993	118.18475787917635
1994	120.34247398498982
1995	126.82660027912942
1996	127.17262097364755
1997	141.67577421896482
1998	130.45450253652453
1999	133.31178383400433
2000	157.8041242211453
2001	168.88973224801737