Think aloud protocol
Think-aloud protocol (or think-aloud protocols, or TAP; also talk-aloud protocol) is a method used to gather data in usability testing in product design and development, in psychology and a range of social sciences (e.g., reading, writing, translation research, decision making, and process tracing). The think-aloud method was introduced in the usability field by Clayton Lewis  while he was at IBM, and is explained in Task-Centered User Interface Design: A Practical Introduction by C. Lewis and J. Rieman. The method was developed based on the techniques of protocol analysis by Ericsson and Simon.
Think-aloud protocols involve participants thinking aloud as they are performing a set of specified tasks. Users are asked to say whatever they are looking at, thinking, doing, and feeling as they go about their task. This enables observers to see first-hand the process of task completion (rather than only its final product). Observers at such a test are asked to objectively take notes of everything that users say, without attempting to interpret their actions and words. Test sessions are often audio- and video-recorded so that developers can go back and refer to what participants did and how they reacted. The purpose of this method is to make explicit what is implicitly present in subjects who are able to perform a specific task.
A related but slightly different data-gathering method is the talk-aloud protocol. This involves participants only describing their action but not giving explanations. This method is thought to be more objective in that participants merely report how they go about completing a task rather than interpreting or justifying their actions (see the standard works by Ericsson & Simon).
As Kuusela and Paul  state the think-aloud protocol can be divided into two different experimental procedures. The first one is the concurrent think-aloud protocol, collected during the decision task. The second procedure is the retrospective think-aloud protocol, gathered after the decision task.
See also 
- Comparison of usability evaluation methods
- Protocol analysis
- Partial concurrent thinking aloud
- Retrospective Think Aloud
- Lewis, C. H. (1982). Using the "Thinking Aloud" Method In Cognitive Interface Design (Technical report RC-9265). IBM.
- http://grouplab.cpsc.ucalgary.ca/saul/hci_topics/tcsd-book/chap-1_v-1.html Task-Centered User Interface Design: A Practical Introduction, by Clayton Lewis and John Rieman.
- Ericsson, K., & Simon, H. (May 1980). "Verbal reports as data". Psychological Review 87 (3): 215–251. doi:10.1037/0033-295X.87.3.215.
- Ericsson, K., & Simon, H. (1987). "Verbal reports on thinking". In C. Faerch & G. Kasper (eds.). Introspection in Second Language Research. Clevedon, Avon: Multilingual Matters. pp. 24–54.
- Ericsson, K., & Simon, H. (1993). Protocol Analysis: Verbal Reports as Data (2nd ed.). Boston: MIT Press. ISBN 0-262-05029-3.
- Kuusela, H., & Paul, P. (2000). "A comparison of concurrent and retrospective verbal protocol analysis". American Journal of Psychology (University of Illinois Press) 113 (3): 387–404. doi:10.2307/1423365. JSTOR 1423365. PMID 10997234.