Thorndike (1920) found officers' trait ratings 'too high and too even' to be independent judgments, naming the global-impression bleed the 'halo' (later crystallized as the 'halo effect')

epistemicscognitive-biassource-evaluationpsychologyhistory-of-sciencepsychometrics

In "A Constant Error in Psychological Ratings" (Journal of Applied Psychology 4(1), 1920), Edward L. Thorndike examined ratings that WWI army officers gave 137 aviation cadets on four supposedly separate traits — Intelligence, Physique, Leadership, and Character — and found the correlations among them "too high and too even" to reflect genuinely independent judgment. A single global impression of each cadet was leaking into every specific trait score: "Obviously a halo of general merit is extended to influence the rating for the special ability, or vice versa." Thorndike found the same pattern in a separate set of 129 teachers' ratings, and prescribed the corrective of rating each quality separately without knowledge of the evidence bearing on any other quality.

This is the paper that coined the term: Thorndike's printed word is halo ("the constant error of the 'halo,' as we may call it," p.28), and the fixed compound halo effect is a later crystallization, not his wording. It is now the vault's oldest primary source on the two-axis source-evaluation cluster. The failure Thorndike documented — a general impression contaminating ratings meant to be independent — is structurally the failure the vault already tracks in modern form: intelligence analysts cannot hold source reliability apart from information credibility, over-weighting a source's global track record, and a language model's authority judgment degrades when fed the document's own content. The army rating instructions Thorndike reproduces in the paper — the official plan "devised by Walter Dill Scott," whose directions "very emphatically required each of these four to be estimated independently of the others" — demanded the same independence the later Admiralty Code would, and produced the same leak. See entity-halo-effect and entity-edward-thorndike.