By studying treatment contrasts and ANOVA models, we propose a
generalized minimum aberration criterion for comparing asymmetrical fractional
factorial designs. The criterion is independent of the choice of treatment
contrasts and thus modelfree. It works for symmetrical and asymmetrical
designs, regular and nonregular designs. In particular, it reduces to the
minimum aberration criterion for regular designs and the minimum
G2 aberration criterion for twolevel
nonregular designs. In addition, by exploring the connection between factorial
design theory and coding theory, we develop a complementary design theory for
general symmetrical designs, which covers many existing results as special
cases.