In Legal Search Exact Recall Can Never Be Known – Part One, by Ralph Losey, e-Discovery Team™

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In legal search you can never know exactly what recall level you have attained. You can only know a probable range of recall. For instance, you can never know that you have attained 80% recall, but you can know that you have attained between 70% and 90% recall. Even the range is a probable range, not certain. Exact knowledge of recall is impossible because there are too many documents in legal search to ever know for certain how many of them are relevant, and how many are irrelevant. I will explain all of these things in this three-part blog, plus show you a new way to calculate probable recall range that I have recently come up with.

Difficulty of Recall in Legal Search

In legal search recall is the percentage of target documents found, typically relevant documents. Thus, for instance, if you know that there are 100 relevant documents in a collection of 1,000, and you find 80 of them, then you know that you have attained 80% recall. . . .