1. Selecting, recruiting and informing users Alfred Kobsa University of California, Irvine

2. Recruiting users How many? –Using 5-8 users will already reveal most major UI problems –Use 3-5 users for each subgroup ( ☛ potentially exponential growth of subject size) –Considerably more if statistically significant differences are at issue Inhouse or external? –Inhouse: confidentiality preserved, good motivation, inexpensive(?), fewer logistics, can be rushed –External: users often more representative, neutral Recruitment channels: announcements (newspaper, posters, online bulletin boards, email, …), word-of-mouth, recruiting agencies, sales / distribution channels state type of product, requirements, duration, location, incentive

3. Selecting and scheduling users “Screener”: set of criteria to help filter participants demographics, skills, contacts to competitors, “odd people”, “professional test users” Screen potential participants on first contact (preferably via phone or in person, 10-15 mins) Send out invitation in writing, and an email reminder on the day before (with directions, phone number for last-minute changes) Over-recruit (?), or better have backup Create an inhouse database of potential subjects (also for tax purposes)

4. Participant incentives Prime motivation to participate should be –being interested in your product (but not too much) –being curious –wanting to help you and others Incentives can also be a motivator, but generally should not be the sole one –“Freebies”, gift coupons, cash,… –Thoughtful selection can be very important Extra stimulus incentive should not be too high Give everyone the same amount (or make sure that participants are not aware of discrimination)

5. Legal requirements Company policies often require subjects to sign liability waivers, video release forms, non-disclosure agreements,… Federal agencies and colleges receiving federal funding: Federal regulations for the protection of human subjects may require informed consent of subjects if scientific research is performed (whose purpose is to enhance human knowledge, and not only to improve a product). Codes of conducts of professional societies (such as the American Psychological Association) may regulate how their members have to carry out human subjects studies.

6. Informed consent Purpose Procedures Risks Benefits, Incentive/Compensation Confidentiality Right to withdraw Consent to being video/audiotaped Retention and “secondary use” of data Point of contact