UX Glossary · T
Think-aloud protocol
Also: Thinking aloud
Asking participants to verbalise their thoughts while working, so reasoning becomes observable.
In a think-aloud protocol, participants say what they are thinking while performing a task: what they are looking for, what they expect, what confused them. It is the standard technique in moderated usability testing.
The method was formalised for psychology by K. Anders Ericsson and Herbert Simon in 1980, who argued that concurrent verbalisation of thought can be a valid data source when the instructions are right.
Why it matters
Behaviour alone is ambiguous. Watching someone hesitate for four seconds tells you something happened; hearing “I’m not sure if this is the total or the amount left to pay” tells you what.
It is the difference between knowing where a design fails and knowing why, which is the difference between a finding and a fix.
Concurrent and retrospective
Concurrent thinking aloud happens during the task and is the default. Retrospective happens afterwards, usually reviewing a recording, and is used where speaking during the task would interfere, for instance in timed or safety-critical work.
Concurrent verbalisation does slow people down, so timings from a think-aloud session should not be treated as performance measurements.
In practice
The facilitator’s discipline is not to help. Prompt with “what are you thinking” when someone goes quiet, and otherwise stay silent. Every explanation offered destroys the finding it was trying to understand.