Minimum support is the lowest fraction of rows in which an item set must occur to qualify as frequent. In Apriori-based outlier detection, it controls which recurring combinations are retained. section 3.2.4
Choose the threshold as a trade-off:
- Raise it to avoid an excessive number of weak item sets, but excessively high values can leave even strong inliers with too few matches. section 3.2.4
- Lower it to retain rarer combinations, but low values can produce meaningless item sets, reduce interpretability, slow execution, and make outliers resemble inliers. section 3.2.4
SpeedDating item sets
Using Apriori with minimum support 0.3 retains combinations occurring in at least 30% of rows. The resulting frequent item sets include ambitious ratings of [0–15] with support 0.797326 and a two-feature combination with support 0.593817.
