Run Chart

A run chart plots a data series in time order with a median line but no control limits. Instead of ±3σ, four formal runs tests check the randomness of the order:

• Clustering — too few runs about the median (points bunch on one side; level shift)
• Mixtures — too many runs about the median (points cross too often; two overlaid sources)
• Trends — too few up/down runs (long monotone streaks; drift, wear)
• Oscillation — too many up/down runs (zig-zag; controller over-correction)