In order to record the users' reactions to the various levels of system interaction, a think-aloud protocol (also called talk-aloud and verbal protocol) was used. Users were asked to describe their impressions, intentions and actions throughout the search session. This commentary was recorded on audio tape recorder to be analysed later, and selected comments were recorded on the observation form so that further explanation could be elicited in the post-test interview.
The co-operative evaluation technique also allows test administrators to elicit comments from participants by verbal and non-verbal prompts. These are not meant to assist the users, but to maintain a continuous dialogue to help them articulate their interaction with and reaction to the system. The prompts were intended to be value-free and generally took a form such as: ``What is the system doing now?'', and ``What do you expect will happen if you click that button?''.