CONDUCTING A TEST #5

Who should be participants?

Who should be participants: They should be representative of the intended users. The participants selected will determine how useful the results will be. When recruiting, user characteristics should also be considered (novice or expert user, children or older adults). The type of compensation and whether participants will be given compensation must also be decided.

The Dumas & Redish (1993) describes the process of selecting test participants. They recommend that a user profile be developed by the marketing, usability and design personnel. This profile can be based on market research, analysis of competitors' products, focus groups, observations, and interviews with prospective users.

The user profile should include two types of characteristics: those that all users will share, and individual characteristics among users. Examples of factors that may be included in a user profile are: work experience, general computer experience; experience with this product, knowledge base, age, and experience with similar products.

Dumas & Redish go on to describe how to divide the users into subgroups and they make an important point that the intermediate users can be left out. By this they mean that the participants from the extremes of the range of participant population will often give you more useful information than those from the middle of the range.

The number of people to include in a subgroup will depend on whether your goal requires a certain number of people and how much budget you have. Neilsen and Molich (1990; in Dumas & Redish) found that almost half of major usability problems were detected with three participants. Other studies found 4 and 5 participants found 90% of the problems. c also state that once there are more than 2 subgroups of 3 to 5 people the same problems arise.