Time-based ad refresh vs event-based refresh

Time-based ad refresh vs event-based refresh

Benchmark drop. Incremental impressions and viewable CPM by trigger (n=95 sites):

— 30s timer (active tab only) $▮▮▮▮▮ +1.4 imps/session
— 30s timer (no active check) $▮▮ wasted, viewability tanks
— User-action (scroll/tab focus) $▮▮▮▮▮▮▮ +1.1 imps, CPM held

Naive timer refresh inflates impression counts but feeds advertisers non-viewable inventory — they detect it and cut bids. Event-based refresh (fires only on engagement) preserves viewable CPM.

Google's policy: minimum 30s and refresh only on user action or active tab. Refresh only the single most-viewed slot, not all.

So what: Active-tab + action-gated refresh vs blind timer — viewable RPM ▲ 11%, policy risk ▼.