Designing an experiment is more than creating stimuli and tasks and deciding onthe participant experience. Before conducting the experiment, the exact form ofdata to be collected needs to be decided, and importantly, it needs to beconfirmed as sufficient for answering the research question.

This chapter focusses primarily on data collection. It describes the differenttypes of data that can be collected for different purposes and the means ofcollecting it.

We make the traditional distinction between quantitative data(represented by numbers; e.g., the number of errors, a preference ranking) andqualitative data (not represented by numbers; e.g., averbal description of problems encountered in performing the task, a videoshowing interaction with an interface).

In practise, there are two distinct decisions to be made about data:

• What data to collect (a decision made in advance of the experiment),and

• How to analyse the data (a decision made after the experiment hasbeen run).

These two decisions are inextricably linked because the potential means ofanalysis will influence the decision on what data to collect. Any discussionabout data collection therefore necessarily entails discussion on how it will beanalysed.