“…The majority of approaches has been based on some form of parametric model. Several have been proposed (Israelsohn, 1960;Marubini, et al, 1972;Bialik, et al, 1973;Bock, et al, 1973;Manwani et al, 1973;Tanner, et al, 1976;Preece and Baines, 1978;Bock and Thissen, 1980;Berkey and Reed, 1987;Byard et al, 1991;Jolicoeur et al, 1992;Qin et al, 1996;Ledford and Cole, 1998). Parametric curve-fitting entails the estimation of a number of unknown constants, which specify the curve.…”