The vocabulary of writing measurement

Plain-English definitions of the terms behind writing measurement, each with real numbers, cited sources, and a worked example.

• Burstiness
  Burstiness measures how much writing varies across a document, most visibly in sentence length and structure. Human writing tends to alternate short and long sentences; AI-generated text is typically more uniform, producing low burstiness.
• Perplexity
  Perplexity measures how predictable a text is to a language model: the average surprise per word. Low perplexity means the model finds each word easy to predict; AI-generated text typically scores lower than human writing.
• Sentence Length Variance
  Sentence length variance measures how widely sentence lengths spread around their average in a passage, reported as variance or standard deviation in words. High variance signals varied rhythm; low variance signals uniform, metronomic prose.
• Flesch Reading Ease
  The Flesch reading ease score rates text readability from 0 to 100 using average sentence length and average syllables per word. Higher scores mean easier reading; 60-69 is standard, readable by high school students.
• Type-token ratio (TTR)
  The type-token ratio (TTR) measures vocabulary diversity by dividing the number of distinct words (types) by the total number of words (tokens) in a text. Higher values mean less repetition; scores are only comparable between equal-length texts.
• Hapax legomenon
  A hapax legomenon is a word that occurs exactly once within a given context: a single text, an author's complete works, or a language's entire written record. From Greek, 'said once'; plural: hapax legomena.
• Function words
  Function words (the, of, and, to, was) carry grammatical structure rather than content meaning. They form a small closed class, used at high frequency and largely unconsciously, which makes their usage rates powerful evidence in authorship attribution.
• Lexical density vs lexical diversity
  Lexical density is the share of a text's words that are content words (nouns, verbs, adjectives, adverbs). Lexical diversity is the range of different words used. A text can score high on one and low on the other.
• Stylometric fingerprint
  A stylometric fingerprint, also called a writeprint, is the measurable pattern of a writer's unconscious habits, from word choice to punctuation, that stays stable enough across texts to identify authorship, much as a physical fingerprint identifies a person.
• Idiolect
  An idiolect is one person's individual version of a language: the vocabulary, grammar, spelling and phrasing habits unique to them. In writing, your idiolect is effectively your fingerprint; no two people use language identically.
• Voice vs tone vs style
  Voice is a writer's stable personality on the page; tone is how that personality flexes for context and audience; style is the concrete, countable choices, such as sentence length and punctuation, that carry both.
• Passive voice
  The passive voice is a grammatical construction in which the subject receives the action rather than performing it, formed with a form of 'be' plus a past participle: 'the report was submitted'. It is a choice, not an error.

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