The definition of the conditions, tasks, and experimental objects is the initialfocus of the experimental design, and must be carefully related to the researchquestion, as described in Chapter 2. The experiment itself could be describedsimply as presenting the stimuli to human participants and asking them toperform the tasks. There are, however, still many other decisions to be madeabout the experimental process, as well as additional supporting materials andprocesses to be considered.

This chapter focuses on the nature of the participant experience, that is, whateach participant will do between the start and end times of the experiment– a lot more happens than simply presenting the trials.

Allocating participants to conditions

As highlighted in Chapter 1, the key issue when running experiments is thecomparison of performance between the conditions: does one condition producebetter or worse performance than another? To determine “performance witha condition,” human participants will need to perform tasks associatedwith the HCI idea being investigated, and measurements of the overallperformance for each condition will be taken. Recall that we want to producedata like that in Figure 2.1, which summarises performance according to eachexperimental condition, with no explicit reference to tasks or experimentalobjects.