Abstract

Using regression equation for short forms of intelligence scales tends to cause over-estimation of the IQ especially for those who have lower intelligence. Such an systematic error in IQ estimation threats the validity of intelligence scale short form. The current study aims to resolve the problem by proposing new way of correction based on RTM amount formula by Davis(1976). To do so, this study compared the accuracies of proration method, linear equating method, regression formula method, regression equation correction by Ehrler et al.(2019) with our correction proposal. Two homogeneous low intelligent groups and a heterogeneous clinical group were tested. As results, the proposed correction method showed better accuracy over regression formula method, better validity over proration method and linear equating method, and more generally applicable over Ehrler et al.(2019)’s correction. The proposed correction method successfully reduced the systematic error of over-estimation for lower intelligence.