This translation has not been editorially reviewed yet. The German version is authoritative. Deutsche Fassung →
Field data and lab data: why two values for the same page
Field data comes from real visitors' browsers over a 28-day window; lab data comes from a single run under fixed conditions. Both are correct, and they measure different things: the field tells you how your visitors are actually experiencing it; the lab tells you whether a change worked.
- Field data only exists once an address has enough visits. New or low-traffic pages have none — that's not an error, it's a statement about the data available. Our report says so explicitly then, instead of presenting the lab value as a field value.
- Lab data is reproducible, and that makes it the right yardstick for before-and-after comparisons. It's not representative, though: a single run with a throttled connection doesn't reflect a user base.
- If the two diverge, that's a clue, not a contradiction — usually the devices, connections, or the actual pages visited differ.
