A travel-planning app may be used in short bursts across a week: on a train, during a conversation with a partner, then again while comparing prices at home. A single interview can recover part of that story, but it asks the participant to reconstruct events that may not have seemed memorable at the time.

A diary study asks participants to record relevant experiences over a period, often close to when they occur. Entries may be written, spoken or visual. The method is useful for investigating routines, changing experiences and activities spread across settings or days.

Choose when an entry should happen

In a fictional travel study, participants might log each occasion when they reconsider an itinerary, or respond to a short prompt each evening. The first approach focuses on a defined event; the second offers a regular opportunity to reflect, including days when nothing happened. Signals at selected times provide another option when the question concerns experiences people might not independently choose to log.

Choose the schedule and duration around the activity, not a standard number of weeks. Nielsen Norman Group’s diary-study guide describes how the method captures experiences over time and in context. An infrequent activity may require a different design from a daily routine.

Define the trigger clearly enough that participants interpret it consistently. “Whenever you feel frustrated” asks for a judgement that may vary widely; “after each attempt to change a booking” supplies a more specific event if that is what the study needs.

Make the recording manageable

Keep prompts focused on the event, circumstances, action and outcome. Test the burden with a small pilot, including how easy it is to make an entry where the activity occurs. Video may be useful for showing an environment, but less practical than a short note on a crowded train.

Agree contact and compensation arrangements in advance. Reminders should support participation without implying that particular experiences or positive answers are preferred. The study should allow people to skip private situations or record only what is appropriate to share.

Entries remain self-reports. Participants can forget, summarise selectively or change their behaviour because they are recording it. Nielsen Norman Group’s discussion of diary-study trade-offs explores the tension between natural behaviour, participation and accuracy.

Analyse both the sequence and the accounts

Read each person’s entries over time before combining material across participants. A concern that disappears after the first day may mean something different from one that accumulates after repeated use. Preserve timestamps and relevant context while developing patterns through an appropriate qualitative approach.

Missing entries need investigation. They may reflect non-use, forgotten logging, technical trouble or withdrawal; treating every gap as inactivity would manufacture a behavioural finding. A closing interview can revisit important entries and clarify omissions, while recognising that retrospective accounts add another perspective rather than a final truth.

A diary study’s longitudinal perspective can reveal moments worth examining through a focused usability test. Its contribution is the pattern of experience across time, including the circumstances a single scheduled session would struggle to reproduce.