[7.x] [ML] Avoid very low p-values if the term is only a tiny fraction of the foreground set (#76764) #76772
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…he foreground set (elastic#76764) Whilst testing the p_value scoring heuristic for significant terms introduced in elastic#75313 it became clear we can assign arbitrarily low p-values if the overall counts are high enough for terms which constitute a very small fraction of the foreground set. Even if the difference in their frequency on the foreground and background set is statistically significant they don't explain the majority of the foreground cases and so are not of significant interest (certainly not in the use cases we have for this aggregation). We already have some mitigation for the cases that 1. the term frequency is small on both the foreground and background set, 2. the term frequencies are very similar. These offset the actual term counts by a fixed small fraction of the background counts and make the foreground and background frequencies more similar by a small relative amount, respectively. This change simply applies offsets to the term counts before making frequencies more similar. For frequencies much less than the offset we therefore get equal frequencies on the foreground and background sets and p-value tends to 1. This retains the advantage of being a smooth correction to the p-value so we get no strange discontinuities in the vicinity of the small absolute and difference thresholds for the frequency.
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@elasticmachine update branch |
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Backports the following commits to 7.x: