Clever and easy mathematics to figure out how many items were not found in discovery, research, review, or other search

A simple formula allows you to calculate the number of relevant documents missed by reviewers, or the precedent cases missed by researchers, or the improper expense records submitted on invoices, or the number of typos in a brief. Curious?

As explained in John D. Barrow, 100 Essential Things You Didn’t Know You Didn’t Know: Math Explains Your World (Norton 2008) at 11, you start by having two people do their best on a search for discovery documents, opinions, billing irregularities, or proofreading catches. You then calculate “the product of the number that each found that the other didn’t divided by the number they both found.” The closer the two people are to finding the same items, the more confident you can be that the unfound items are few; conversely, if each found many items not found by the other, the unfound items will be much more numerous. With this formula, you can at least size the gap.