Reference table
Support, confidence and lift: what each one hides
The three association rule metrics in market basket analysis, and where each misleads
A reference table for the three numbers behind every association rule in market basket analysis. Support counts how often a pair appears, confidence how often Y shows up when X does, and lift compares co-occurrence with chance. Each has a known trap, from popular items crowding out rare pairs to lift exploding on a handful of baskets. Useful for analysts and merchandisers who present basket rules to decision makers.
Where this appears
What's in this reference table
| Metric | Formula | What it measures | The trap |
|---|---|---|---|
| Support | P(X and Y) | How often the pair appears at all | Popular items dominate, and rare but valuable pairs fall below any sensible threshold |
| Confidence | P(Y given X) | How often Y shows up when X does | Ignores how common Y is on its own |
| Lift | P(X and Y) / (P(X) x P(Y)) | Co-occurrence versus statistical independence | Explodes on rare items that coincided a handful of times |
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<a href="https://www.koji.so/visuals/support-confidence-lift-market-basket-metrics"><img src="https://www.koji.so/visuals/support-confidence-lift-market-basket-metrics/support-confidence-lift-market-basket-metrics.png" alt="Table of the three market basket analysis metrics, support, confidence and lift, with each formula, what it measures and its trap." width="1200" height="715" /></a>
<p>Source: <a href="https://www.koji.so/visuals/support-confidence-lift-market-basket-metrics">Support, confidence and lift: what each one hides</a>, Koji</p>
