Abstract: In this paper, we list some new orthogonal main effects plans for three-level designs for 4, 5 and 6 factors in 18 runs and compare them with designs obtained from the existing orthogonal array. We show that these new designs have better projection properties and can provide better parameter estimates for a range of possible models. Additionally, we study designs in other smaller run-sizes when there are insufficient resources to perform an 18-run experiment. Plans for three-level designs for 4, 5 and 6 factors in 13 to 17 runs are given. We show that the best designs here are efficient and deserve strong consideration in many practical situations.
Key words and phrases: Factor screening, fold-over designs, fractional replicate, orthogonal array, projection.