Orthogonal arrays with mixed levels are very useful in factorial experiments when factors with different numbers of levels are to be investigated. However, one limitation associated with mixed-level orthogonal arrays is that many of them require a large number of runs. In such cases, nearly orthogonal arrays - which generally use fewer runs by slightly relaxing the requirement of orthogonality - may be useful. We propose a definition of nearly orthogonal arrays of strength m, extending the concept of orthogonal arrays of strength m. We focus on the nearly orthogonal arrays involving 2- and 3-level factors with small run sizes. Some useful arrays are tabulated for practical use. These designs are shown to have nice statistical and combinatorial properties.
- Nearly Orthogonal Array of Strength m
- Orthogonal Array