Miller's 1956 'channel capacity of absolute judgment' sets an information-theoretic ceiling on how many categories a single-dimension rating scale can carry

information-theorypsychophysicshistory-of-psychologysource-evaluationepistemicsrating-scales

In "The Magical Number Seven, Plus or Minus Two" (Psychological Review 63:81–97), George A. Miller imports Shannon's information theory into psychophysics to explain a recurring empirical ceiling: when people make absolute judgments along a single dimension — pitch, loudness, position, saltiness — the amount of information they can transmit about the stimulus saturates around a handful of distinguishable categories, roughly seven plus or minus two. Miller names the ceiling directly: it is "the channel capacity of the observer: it represents the greatest amount of information that he can give us about the stimulus on the basis of an absolute judgment."

The move is to treat a human rater as a communication channel. Stimulus variance is the input; the rating is the output; "amount of transmitted information" is the psychological analogue of the covariance between them, and channel capacity is the asymptote — add finer input distinctions past that point and the output stops carrying them. The category count of any single-axis rating scale is therefore not a free design choice but is bounded by what absolute judgment can resolve.

This is the buried explanatory layer beneath a whole cluster of rating-scale claims the vault built from the other end. The Admiralty Code's six-level scales are exactly the kind of single-axis absolute judgment Miller's ceiling governs, and Samet's 1975 argument for finer intelligence-rating scales applies this tradition explicitly, citing Bendig (1954) that a nine-point scale transmits more information than a five-point one. The lineage — Miller through Bendig to Samet — is drawn out in observation-admiralty-code-scale-length-descends-from-millers-channel-capacity.