CC-08
Std Dev Band Widening Over Time
Control Chart
Default severity: medium
ProcessMetricsOutputRisk
What it detects
Standard deviation band is expanding across consecutive windows — process becoming less predictable over time.
Detection formula
FOR each_window W: band_width(W) = UCL(W) - LCL(W) IF linear_regression(band_widths).slope > 0 AND p_value \< config.cc.trend_significance // default: 0.05 THEN FLAGExamples in practice
- 3–6 weeks
- Rolling averages, control limits, or band width diverge from expected statistical bounds.
- Recent control-chart windows show drift, clusters, or missing limit configuration.
Suggested response
Treat the metric as a control signal: confirm limits, windows, and cross-team spread before acting.
Coaching playbook
Symptom
Standard deviation band is expanding across consecutive windows — process becoming less predictable over time.
Why it matters
When "Std Dev Band Widening Over Time" keeps appearing, the team is signalling a repeatable process gap. Left unexamined, the pattern hides where work really stalls and makes improvement metrics harder to trust.
What you can achieve
Treat the metric as a control signal: confirm limits, windows, and cross-team spread before acting.
Facilitation questions
- What system change would stop "Std Dev Band Widening Over Time" from firing again?
- What do the cited issues have in common — same root cause or same workaround?
- Who owns the two-week experiment and how will we verify on the next import?
Run this rule against your own tracker data with Flow Analyzer.