Two production measurements can move together for reasons that are not captured in the chart. A visible relationship is a starting point for investigation.
ASQ describes scatter diagrams as tools for examining relationships between paired variables. ASQ — Scatter Diagram.
Preserve the pairing
For a process study, make sure each pair belongs to the same relevant observation and condition. Combining values from different items or periods can create a relationship that does not describe the intended process.
Investigate alternatives
Consider shared influences, measurement issues and changes in the process. Do not turn a fitted line into an automatic instruction to change a material or setting. The action needs evidence addressing the proposed causal explanation.
Source reviewed 25 October 2026. Interpretation and original diagrams: PLUSHIP / Qunhe. Examples are illustrative.
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