A comparison of location effect identification methods for unreplicated fractional factorials in the presence of dispersion effects

Unreplicated fractional factorial designs are usually used to identify location effects and dispersion effects in screening experiments. Various methods for identifying active location effects have been proposed during last three decades. All of these methods depend on the assumption of no dispersion effects. Meanwhile most of the dispersion-identification methods rely on first identifying the correct location effect model. The presence of dispersion effects induces correlation among location effect estimates. If location-effect identification methods are sensitive to this correlation, then finding the correct location model may be more difficult in the presence of dispersion effects. The primary aim of this project is to compare the robustness of different location-identification methods - Box and Meyer (1986), Lenth (1989), Berk and Picard (1991), and Loughin and Noble (1997) - under the heteroscedastic model via simulation studies. Confounding of location and dispersion effects has also been investigated here.