Year	Number
1961	66.6684350132626
1962	66.45994832041343
1963	65.4911838790932
1964	65.35626535626535
1965	65.85956416464892
1966	65.10538641686182
1967	64.98855835240275
1968	63.982102908277405
1969	64.33260393873084
1970	64.23982869379014
1971	64.15094339622641
1972	64.18219461697723
1973	65.0103519668737
1974	64.09736308316431
1975	64.90872210953347
1976	66.5314401622718
1977	66.93711967545639
1978	67.34279918864098
1979	67.34279918864098
1980	66.73453093812375
1981	64.33398821218074
1982	62.823984526112184
1983	60.049523809523805
1984	59.572232645403375
1985	58.78003696857671
1986	58.561020036429866
1987	57.07885304659498
1988	57.03886925795053
1989	58.39721254355401
1990	59.72508591065292
1991	61.016949152542374
1992	62.257525083612045
1993	63.48184818481848
1994	64.03225806451613
1995	65.91639871382637
1996	61.96764705882353
1997	64.27428571428571