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2^k factorial DOE analysis

2^k factorial DOE analysis estimates main effects and interactions from a two-level designed experiment, ranks them on a Pareto chart of standardized effects, and reports main-effect means.

What is 2^k factorial DOE analysis?

In a 2^k factorial experiment every factor is run at two levels and all combinations are covered, so each effect is estimated from all runs simultaneously — vastly more efficient than one-factor-at-a-time, and the only way to see interactions. Factors are coded −1/+1; the effect of a term is 2× its regression coefficient: the average change in response from the low to the high level.

With replication, effects get t-tests from the residual variance. In an unreplicated saturated design there are no residual degrees of freedom, so Lenth's pseudo standard error (a robust estimate from the smaller effects themselves) provides the yardstick — the standard approach for screening designs.

The Pareto chart of |standardized effects| with a significance cutoff is the classic readout: active factors stick out past the line.

When should I use 2^k factorial DOE analysis?

  • Analyzing a designed 2-level experiment (screening or characterization).
  • Finding which factors and interactions actually move a response.

What data does it need?

A numeric response + ≥ 2 factor columns each with exactly 2 levels + the interaction order to fit.

What does it report?

Effect / SE / t / p per term, R², a Pareto chart of standardized effects with the α = 0.05 cutoff, and low/high means per factor.

What does it assume?

  • Each factor has exactly two levels; the design covers the combinations (a full or regular fractional factorial).
  • Roughly constant error variance across runs.
  • Lenth-based inference assumes effect sparsity (most effects are null).

How do I interpret the result?

A large interaction means those factors must be set jointly — read the interaction before interpreting its main effects. Level ordering is inferred (numeric content, low/high vocabulary, else alphabetical), so check the low → high direction in the means table.

See also

References

  • Box, Hunter & Hunter (2005). Statistics for Experimenters, 2nd ed.
  • Lenth (1989). Quick and easy analysis of unreplicated factorials. Technometrics 31.