Statistically improbable phrase

A statistically improbable phrase (SIP) is a phrase or set of words that occurs more frequently in a document (or collection of documents) than in some larger corpus. Amazon.com uses this concept in determining keywords for a given book or chapter, since keywords of a book or chapter are likely to appear disproportionately within that section. Christian Rudder has also used this concept with data from online dating profiles and Twitter posts to determine the phrases most characteristic of a given race or gender in his book "Dataclysm". SIPs with a linguistic density of two or three words, adjective, adjective, noun or adverb, adverb, verb, will signal the author's attitude, premise or conclusions to the reader or express an important idea. 
Example.
In a document about computers, the most common word is likely to be the word "the", but since "the" is the most commonly used word in the English language, it is probable that any given document will have the word "the" used very frequently. However, a phrase like "explicit Boolean algorithm" might occur in the document at a much higher rate than its average rate in the English language. Hence, it is a phrase unlikely to occur in any given document, but "did" occur in the document given. "Explicit Boolean algorithm" would be a statistically improbable phrase.
Statistically improbable phrases of Darwin's "On the Origin of Species" could be: "temperate productions, genera descended, transitional gradations, unknown progenitor, fossiliferous formations, our domestic breeds, modified offspring, doubtful forms, closely allied forms, profitable variations, enormously remote, transitional grades, very distinct species" and "mongrel offspring". 
More examples of SIPS are circuitous pandemic, prevailing dominant basal paradigm, irrefutable scientific proof, cell signalling process, nuclear DNA transduction, instructive cooperative interaction, septarian concretions, dying economic system, Western block collapse, the free enterprise system, subsequent enabling legislation, totalitarian political ideology, pernicious financial racket, bottomless degeneracy, widespread censorship, moral highground, shifty-eyed demagogue, arrogant entitled narcissist, scheming sociopath, predatory psychopath, personal moral failings, disinterested curiosity, countless disasters and unthinkable suffering, innumerable cosmoi, zero-based budgeting, gut-wrenchingly gruesome gangsters. 