WH-AS5 - Intervention Trade-Off Analysis
Aims
Compare the individual and combined effects of the storage assignment, layout, and picking interventions developed in AS2 through AS4. Use the activity profiles and baseline from AS1 to evaluate warehouse performance, feasibility, and resource requirements. Recommend a feasible course of action and explain its trade-offs and limitations.
Your proposed approach does not need to perform better than the baseline. Scientific reporting includes findings that do not support the expected outcome, including null results.1 As Thomas A. Edison put it during his storage-battery experiments:
“I know several thousand things that won’t work.”2
If an expected improvement does not occur, report that negative result. Report the evidence factually, including unchanged or worse performance. Explain the performance gap as far as your evidence allows. Distinguish supported explanations from hypotheses, and suggest changes or further experiments that could improve performance. Keep the comparison fair.
Learning objectives
After completing this assignment, you will be able to:
- define compatible scenarios from storage, layout, and picking decisions;
- distinguish isolated intervention effects from combined design effects;
- assess performance and resource trade-offs under common assumptions; and
- justify a feasible recommendation using sensitivity results and limitations.
Study case
Use the same SPR warehouse, cleaned data, activity profiles, and baseline as in AS1 through AS4. Table 25.1 identifies the earlier results used in the comparison.
| Earlier analysis | Use in the intervention comparison |
|---|---|
| WH-AS1 - Diagnosis and activity profiling | Baseline conditions, demand, activity profiles, and KPIs that define the problems and evaluation scope. |
| WH-AS2 - Storage location assignment and space requirements | Current and proposed assignments, storage requirements, and replenishment and capacity constraints. |
| WH-AS3 - Warehouse Layout Improvement | Current and proposed layouts, space use, distances, handling interfaces, and feasibility conditions. |
| WH-AS4 - Order-Picking Improvement | Picking strategies and performance estimates for the current warehouse and retained designs. |
State the assumptions, missing inputs, and feasibility limits that affect the comparison. Distinguish observed warehouse facts from assumptions and calculated results.
Compare the interventions and their combinations
Compare the baseline, isolated interventions, and retained combinations of storage assignment, layout, and picking decisions. A combination of changes may perform better than any isolated intervention, or introduce costs and constraints that outweigh its benefits. Identify the feasible option that best meets your chosen objectives, based on the evidence.
Figure 25.1 shows an example with one baseline and one proposed option for each decision. The three choices produce eight configurations, listed in Table 25.2. Activity profiling provides the common data and operational diagnosis for all scenarios.
The labels S0 through S7 are short identifiers for the scenarios in this example. S0 identifies the current situation, and each other label identifies a specific combination of decisions. The numbers do not rank performance.
You may choose descriptive names such as “Current warehouse”, “Picking change only”, or “New layout with revised storage and picking”. Define the layout, storage assignment, and picking policy for each scenario.
| Scenario | Layout (AS3) | Storage assignment (AS2) | Picking (AS4) |
|---|---|---|---|
| S0 | Baseline | Baseline | Baseline |
| S1 | Baseline | Baseline | Proposed |
| S2 | Proposed | Baseline | Baseline |
| S3 | Proposed | Baseline | Proposed |
| S4 | Baseline | Proposed | Baseline |
| S5 | Baseline | Proposed | Proposed |
| S6 | Proposed | Proposed | Baseline |
| S7 | Proposed | Proposed | Proposed |
S1, S2, and S4 isolate picking, layout, and storage changes relative to S0. S3, S5, S6, and S7 combine changes. S7 need not be the best scenario. If you retain more than one proposed option, extend the scenario definitions and explain which options you compare.
Check scenario compatibility
The order of analysis depends on the design decisions. A new layout may need a new product assignment before picking can be evaluated.
For example, a proposed reserve and forward-picking arrangement creates areas that must be populated with products. Apply and justify a suitable assignment strategy, heuristic, or optimization model for those areas before evaluating the picking operation. Use the resulting product locations, aisle geometry, depots, capacity, and replenishment interfaces in the picking analysis.
When applying a baseline storage assignment or picking policy to a proposed layout, explain how it operates there. Check compatibility and explain any changes needed. If the current product assignment or picking policy cannot operate in the new layout, record that combination as infeasible or explain why you exclude it. Keep the observed current situation identifiable as the baseline under your chosen scenario name.
Evaluation requirements
Evaluate the retained combinations of layout, storage assignment, and picking decisions. For each scenario, state the assumptions, resource requirements, and feasibility status. Compare its performance with S0 and quantify the differences. Include failed or infeasible evaluations and explain their status. Distinguish unavailable results from zero values.
Use the same product population, workload, demand period, units, and evaluation assumptions across scenarios. Include uncertainty and sensitivity results where they affect the recommendation.
Compare scenarios that differ in one decision to understand the effect of that decision under the other settings. For example, S0 versus S1 measures a picking change in the current design, while S6 versus S7 measures that picking change with the proposed storage and layout. S0 versus S7 measures the combined change. Explain why the combined effects differ from the effects of isolated interventions. Account for changes in replenishment, capacity, labor, equipment, or service where relevant.
Management recommendation
Recommend a feasible scenario, or explain the conditions under which you would choose between alternatives. Explain the performance differences, resource requirements, feasibility conditions, and limitations that support your choice. Prioritize the proposed actions, explain their implementation sequence, and identify what management should monitor. Limit claims about the best solution to the alternatives and assumptions evaluated. Claim global optimality only when your method and evidence establish it.
Assessment criteria
Table 25.3 gives the rubric for the comparison and management synthesis developed in AS5. Each criterion is worth 2 points, for a total of 10 points.
- 2 points: complete, correct, and decision-relevant evidence.
- 1 point: partially convincing evidence with a material omission, weakness, or minor error.
- 0 points: missing evidence or evidence that is materially incorrect, infeasible, or unsupported.
| Criterion (2 points each) | Evidence expected for full credit |
|---|---|
| Fair comparison | Product-assignment, layout, and picking interventions are compared using consistent baselines, demand, units, and constraints. |
| Performance trade-offs | Effects on cost, throughput, space, service, workload, and risk are quantified where the evidence permits. |
| System interactions | Complementarities, conflicts, and shifted burdens across the three interventions are identified. |
| Uncertainty and robustness | Material assumptions, sensitivities, data limitations, and implementation risks are tested or bounded. |
| Management synthesis | The report provides a concise, prioritized course of action with conditions, sequencing, and monitoring indicators. |
For report format and reproducibility requirements, see the project file requirements.
References
See the Nature editorial on null results and Recommendation 8 of the National Academies report on research integrity (Nature 2020; National Academies of Sciences, Engineering, and Medicine 2017, Recommendation 8).↩︎
An account by Edison’s associate W. S. Mallory appears in Chapter XXIV, “Edison’s Method in Inventing” of Edison’s authorized biography (Dyer and Martin 1910, chap. 24).↩︎