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Culturomics investigates historical patterns through large-scale quantitative analysis of recorded language, especially digitized books. A text corpus turns occurrences of words or n-grams into measurable time series. Jean-Baptiste Michel and collaborators demonstrated the approach with a corpus of 5,195,769 books, selecting material partly by the quality of optical character recognition and publication metadata.^[ref]

For an original example, 500 occurrences in ten million word tokens give $500/10^7=5\times 10^{-5}$. A later collection with 800 occurrences in twenty million tokens gives $4\times 10^{-5}$: the count rose, but the normalized rate fell. A changing name can also change the measured series without an equivalent change in its referent. Culturomics therefore connects computational counting to hypotheses about language change, while requiring checks on publication selection, transcription errors and changing terminology.

Jean-Baptiste Michel helped develop quantitative analysis of large digitized text collections. He is a lead and corresponding author of the study introducing culturomics, which examined changes in language and recorded culture using a large book corpus.^[ref]

A central measurement is relative word frequency: occurrences of a word or phrase in books assigned to a year are normalized by the number of corresponding word sequences in that year's corpus. A raw count can rise merely because more text was digitized. For an elementary illustration, one hundred occurrences among a million tokens and two hundred among four million tokens represent a halving of relative frequency, despite the doubled count.

The data measure the contents of a sampled textual archive. Book selection, date metadata and recognition errors can affect the apparent history of a word; frequency is not a direct measurement of how many people held a belief. The study's contribution was to make large-scale temporal comparisons computationally tractable and quantitatively inspectable, while exposing the importance of the observation process.^[ref]