This question evaluates a data scientist's ability to analyze experimental results, reason about causal inference and subgroup heterogeneity, and interpret CTR lifts in ad-ranking contexts, and is categorized under Analytics & Experimentation.

You ran a standard A/B experiment for a new ad-ranking algorithm. The primary metric is CTR (clicks ÷ impressions). The experiment shows:
Assume randomization at the user level, with typical ad auction dynamics and repeated exposures per user.
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