Seven Points Trending

Seven Points Trending is an SPC (Statistical Process Control) rule detecting systematic process drift when seven or more consecutive points show a consistent upward or downward trend.

## What Is the Seven Points Trending Rule?

  • Trigger: 7+ consecutive points each higher (or lower) than previous
  • Signal: Process shift in progress, not random variation
  • Action: Investigate before out-of-control condition develops
  • Rule Origin: Western Electric / Nelson rules for control charts

## Why Seven Points Trending Matters

Random variation rarely produces seven consecutive moves in one direction (probability <1%). This pattern indicates assignable cause requiring intervention.

Control Chart with Trending Pattern:UCL ───────────────────────────────── ● ● ● ● ← 7-point upward trend ● ●CL ───────────●────────────────────── ●LCL ───────────────────────────────── 1 2 3 4 5 6 7 8 9 10 11Points 3-9: Each higher than previous → Trigger rule

Common Causes of Trending:
- Tool wear (gradual degradation)
- Chemical depletion
- Temperature drift
- Operator fatigue across shift

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