Click-Through Rate CTR (aka "click rate"; email uses CTR distinct from CTOR)
The share of ad views that resulted in a click.
The fork, why two teams get different numbers
Two arguments live inside CTR. First, the DENOMINATOR: clicks / served
impressions vs clicks / measured (or viewable) impressions, viewability-
based CTR is higher because the base is smaller. Second, the NUMERATOR unit:
total clicks vs UNIQUE clicks (one user clicking twice), and in email,
"clicks" (any link) vs "click-to-open rate" (clicks / opens), which is a
completely different ratio. A display team, a paid-social team, and an email
team all say "CTR" and mean three denominators.
The trap
Invalid traffic distorts CTR in both directions: click-bots inflate it, and accidental "fat-finger" mobile clicks inflate it without intent, while counting only the served base understates it.
- The full trap, worked on a real export
- Every formula variant, spelled out
- The reconciliation anchor, what to tie it to and when to refuse
Reference: IAB/MRC Click Measurement Guidelines (reference)