A Technique for Computer Detection and Correction of Spelling Errors (1964)

> In the retrieval system for which it was originally devised, the errors are introduced at various points in the system flow. Some are introduced by equipment, particularly paper tape equipment; some by transcription from source document to a card punching form or card form to punched card; and others by human misspelling.

> ...An inspection of those items rejected because of spelling errors showed that over 80 percent fell into one of four classes of single error-one letter was wrong, or one letter was missing, or an extra letter had been inserted, or two adjacent characters had been transposed.

https://dl.acm.org/doi/10.1145/363958.363994