For experimental or quasiexperimental research with pretests, it was proposed that the pretest should be taken into consideration instead of using the posttest in order to mitigate possible selection bias (Furtak, Seidel, Iverson, & Briggs, 2012; Morris, 2008). Hence, the formula developed in Comprehensive Meta Analysis (version 2.0) was used to obtain effect sizes for
research with pre- and posttests: