A fractional factorial runs a carefully selected half, quarter or smaller fraction of a full two-level factorial. Seven factors can be screened in 8 runs instead of 128, at the cost of aliasing: some effects can no longer be separated from others. The fraction is defined by generators such as E = ABCD, and the design's resolution states which effects are mixed. Screening designs such as Plackett-Burman push the idea further, fitting 11 factors into 12 runs.
Half fraction of five factors gives us resolution V, so two-way interactions are clean. Sixteen wafers, done in a day.
Also heard as
- fractional factorial
- fraction
Related terms
Aliasing
Situation in a fractional design where two or more effects leave identical patterns in the data and cannot be told apart.
Resolution
Rating of a fractional factorial design, in Roman numerals, that states which effects are aliased with which.
Factorial design
Experiment that runs every combination of the chosen factor levels, so each main effect and interaction can be estimated.
DOE
Design of experiments: planning a set of runs that vary several factors at once so their effects can be separated.