research methods
Diary studies
What is a diary study and when should you use one?
A diary study asks participants to log their experiences themselves, in the moment, over days or weeks - capturing what happened, when and how it felt, as life actually unfolds. It trades the one-shot snapshot of an interview for a record over time, which is the only way to study habits, long arcs and infrequent events without relying on faulty memory.
Also known as: diary studies, diary study, experience sampling, longitudinal study
The demo
A new user's first week with an app. Compare the diary they kept as it happened with the one-line summary they'd give you afterwards - and see which one you'd want to design from.
What this demo shows (text version)
A participant's first week with an app is shown two ways. The "in-the-moment diary" is a series of dated, time-stamped entries capturing real moments and feelings as they happened: Monday's hopeful setup, Tuesday's 7am frustration when a sync failed, a small Thursday win, a Sunday "gave up again". The "end-of-week recall" is the single summary they'd give in an interview afterwards: "Yeah, it was mostly fine, took a bit to get going."
The diary preserves the texture, the emotional ups and downs and the specific failure points; the recall flattens all of it into a vague average, because memory smooths and forgets. That's why diary studies suit anything longitudinal, emotional or infrequent, and why they sidestep recall bias. The catch is participant burden, so keep entries quick and expect to support and prompt people throughout.
Diary studies capture behaviour and feeling as they happen, over time, in real life - so they beat one-off interviews for anything longitudinal: habit formation, onboarding over weeks, rare events, changing emotions. By logging in the moment, they sidestep recall bias. The cost is commitment and drop-off, so keep entries quick, prompt people, and expect to support participants through the study.
The week of little in-the-moment notes - the 7am frustration, the small Thursday win, the Sunday "gave up again" - told a story the single end-of-week summary completely flattened. Asked to recall it later, all that texture collapsed into "yeah, it was mostly fine." Capturing the moments as they happen is exactly what a diary study is for.
Diary studies shine where a snapshot can't reach: anything that plays out over time (learning a tool, forming or breaking a habit, an onboarding journey), anything emotional that shifts, and anything too infrequent to catch in a session. Because entries are made in the moment, they largely escape recall bias - you get the Tuesday-morning reality, not a smoothed memory of it.
The method's enemy is participant burden. Logging takes effort, motivation fades, and drop-off is real - so keep each entry tiny (a photo, a quick voice note, a one-tap rating), prompt people at the right moments, make it easy on their own phone, and budget for hand-holding and incentives. A diary study lives or dies on how light you make the act of recording.
It pairs naturally with a follow-up interview: the diary surfaces the moments and patterns, then you sit down and dig into the why behind the entries. And it feeds journey maps and personas with something rare - real, time-stamped, lived experience rather than a single recalled account.