Is watch time a clean signal of viewer preference on YouTube Shorts? What do YouTube researchers report?

A Sept 2026 preprint by authors reporting online A/B tests on YouTube Shorts (Chang et al., arXiv 2609.32839v1; abstract read) states that watch-based signals are confounded by measurement factors: the same watch time implies different preference for videos of different lengths, ratio metrics (percentage watched) systematically favour short videos, and observed behaviour can reflect enjoyment, passive consumption or inattention. Their Factorized Latent Value Model separates confounders (duration, user propensity, session context) from preference and reportedly lifted a primary viewer-enjoyment metric by 2.67% in online A/B tests. Implication for creators reading retention reports (C3-B336-01): raw average view duration and percentage viewed are not directly comparable across lengths, and the recommender itself is being tuned to discount such artifacts; optimizing a short length only to inflate percentage watched is not supported by this work. A companion YouTube Music study (2607.23749) reports that serving-time boosts are neutralized by continuously trained ranking loops. Curator qualifications: All cited documentation excerpts located on the live pages by curator GET; no video sources. Preprint; abstract read only (curator located the abstract statements); not peer reviewed; observational unless stated. Limitations: Abstract-only; deployment status of FLVM in production not stated; author affiliation inferred from Shorts A/B access. Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

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