A diary study is a qualitative research method where consumers record their real-world experiences, thoughts and behaviour around a product, brand or activity over a set period of days or weeks. Learning how to do diary studies with consumers comes down to five things: a decision the study informs, a logging protocol, a small motivated panel, prompts people can answer in under two minutes, and a habit of reviewing entries every day while fieldwork is still open.
The method is worth the effort because it kills recall bias. A consumer asked last week what influenced their last grocery run reconstructs a tidy story. The same consumer writing it down at 6pm on Thursday, with a photo of the shelf and a note about the price they went back for, gives you the real thing: context, hesitation, emotion and the sequence of small decisions that a survey or a 45-minute interview flattens.
It is also the most underestimated amount of work on this list. Zalando’s published gift-shopping diary study ran 12 testers for two weeks and asked each of them for 20 entries. Their team described the daily phase as quite laborious, and only judged continuous categorisation of entries worth doing in hindsight. Plan for real researcher hours across the fieldwork window, not just for the design phase.
This guide walks through the whole process: what to set up first, the eight steps from research question to readout, and the mistakes that quietly ruin an otherwise sound study.
Table of Contents
- What You Need
- Diary format changes what you get back
- Step-by-Step
- How to Do Diary Studies With Consumers: Step 1 — Turn a Business Problem Into a Behavioral Question
- How to Do Diary Studies With Consumers: Step 2 — Pick the Diary Format
- How to Do Diary Studies With Consumers: Step 3 — Recruit Participants, Consent Them and Set the Incentive
- How to Do Diary Studies With Consumers: Step 4 — Write Prompts People Can Actually Answer
- How to Do Diary Studies With Consumers: Step 5 — Pilot Before You Deploy
- How to Do Diary Studies With Consumers: Step 6 — Run Fieldwork and Keep People Completing Entries
- How to Do Diary Studies With Consumers: Step 7 — Code and Condense the Entries
- How to Do Diary Studies With Consumers: Step 8 — Read the Findings and Report Them
- Common Mistakes
- Frequently Asked Questions
- How many participants do you need for a diary study?
- How long should a diary study run?
- Are paper diaries better than app or chat-based diaries?
- How much should you pay participants?
- How do you analyse diary study data?
- What should you ask participants to record?
- Conclusion: What To Do First
What You Need
Most of what you need exists before a single participant is recruited. The list below is deliberately short, because diary studies fail more often on preparation than on method.
A decision, not a curiosity. Write down the decision this study will feed into. Will it shape a service change, a campaign, a product roadmap decision, or a range plan? If nobody can name what changes depending on the answer, cancel it or turn it into a research question with a defined scope.
A logging protocol. There are three standard ones and you pick before recruitment, not after. Interval-based logging asks for entries at fixed times (end of day, after a specific routine). Event-triggered logging asks for an entry whenever something happens, such as each purchase or each meal. Signal-based logging sends an unprompted prompt at random moments, which reaches behaviour people do not think of as reportable. The design research handbook approach names all three and recommends a defined protocol over free-form journalling.
A participant profile and a screener. Decide who the panel needs to be before you write questions. For a study about switching between supermarket brands, that means the person who does the weekly shop, not a general adult panel.
Consent and privacy materials. Diaries collect unusually intimate material: photographs of kitchens, receipts, screens, sometimes other people in the background. Your consent form has to cover that specifically, state how long you hold the data, and give a real route to deletion.
An incentive structure. Pay for completing the study, not for volume. A structure that pays more per entry quietly pushes people to write longer entries and to stretch for material they did not experience, which corrupts exactly what you are measuring.
A coding scheme and a daily review slot. Have a provisional codebook and roughly 20 minutes a day blocked out while the study is live.
Tooling. A dedicated app, a chat channel, a web form, or paper. What you choose changes the burden, the recall quality, the privacy exposure, the setup cost and the kind of evidence you get back.
Diary format changes what you get back
Paper diaries suit low-tech, private categories and participants who dislike phones. They also create recall delay, transcription effort on your side, and no media.
App and web-form diaries give you timestamps, media upload, geo or context fields, and automatic reminders. Setup takes longer and participants need a reliable phone.
Chat-based diaries on Messenger or WhatsApp have become a practical option because most people already answer messages. They lower participation friction, but they generate a chat transcript you must manage carefully, and conversational tone can pull answers away from the prompt. Clicked has written about running WhatsApp-based behavioural studies and finding outcomes they did not expect.
Photo, audio and video diaries capture things text cannot: how a person physically uses a product, the state of their kitchen, the tone of a voice when something is confusing. They raise consent and storage complexity, and they need a clear rule about what must never be photographed, such as other people or account numbers.
Step-by-Step
How to Do Diary Studies With Consumers: Step 1 — Turn a Business Problem Into a Behavioral Question
Start with the business problem in plain language, then narrow it to something a diary can actually observe. “Why are we losing shoppers at checkout” is too broad. “How do first-time buyers of a grocery subscription experience the moment they decide whether to keep it after week two” is observable, bounded and answerable.
Define the participant profile next: category buyer, frequency of the behaviour, and anything that must be true for the behaviour to occur at all during the study window. If you need ten purchases and the panel buys twice a month, the study is mis-specified and no amount of prompting will fix it.
Then name the decisions or moments the diary should observe. Pick two to four. Every extra focus dilutes completion and analysis.
How to Do Diary Studies With Consumers: Step 2 — Pick the Diary Format
Choose based on the behaviour, not on what your tool of choice supports best. Event-triggered logging fits purchases and problems as they happen. Interval logging fits routines and consumption habits where no single moment matters. Signal logging fits emotional, low-salience states that people never think to record.
Match the media to the question: text for reasoning and preference, photos for context and physical use, audio for tone, video for sequence of actions. A mixed format is normal, but cap it at two media types or completion collapses.
Decide the entry frequency before you write any prompts, and write the cap into the consent material so it is not a surprise.
How to Do Diary Studies With Consumers: Step 3 — Recruit Participants, Consent Them and Set the Incentive
Write a short screener that confirms the behaviour is real, not that the participant sounds interested. Ask when they last did it, how often, and what they bought. Recruit a panel with a mix of heavy and light users where the spread matters to your question.
Brief them plainly: what the study is, how many entries are asked for, roughly how long each takes, what happens to their photos, who sees the material, what the payment is and when, and that they can stop or ask for deletion at any point. Informed consent is worthless if the incentive feels like pressure.
That is the real ethical risk in diary studies. A participant who feels the payment depends on a long, personal entry will give you a long, personal entry, and you will read it as signal. Structure payments on completion of the agreed number of entries, keep any bonus tied to finishing rather than to length, and accept the shorter entry as valid data.
How to Do Diary Studies With Consumers: Step 4 — Write Prompts People Can Actually Answer
Prompt wording is the single most common failure point. Practitioners post on research forums asking how to phrase diary prompts because vague prompts reliably produce vague entries, and that is the least fixable problem in the whole study because you cannot re-ask two weeks later.
A workable prompt captures six things and stays under two minutes: the situation, the behaviour, the thoughts, the emotion, the decision point, and one detail that makes it checkable later. Then stop asking.
A prompt that fails: “Tell us about your shopping experience.” A prompt that works: “It’s [time] and you are about to do your weekly shop. Where are you physically, what are you buying first, and what made you choose that?”
Ten prompts you can adapt:
- It is [time] and you are about to [activity]. Where are you and what are you doing right now?
- What did you do first, and why that before anything else?
- What almost stopped you just now?
- How did you feel at that moment, in one word plus a sentence?
- What did you expect to happen, and what happened instead?
- What did you check, compare, or look up before deciding?
- If a photo or screenshot helps, add it. Do not include anything that identifies you or anyone else.
- Who else was involved, and what did they say or do?
- What did you pay, and what would you have paid?
- What will you do differently next time?
Ask the same core questions every time so entries are comparable, and vary only the situation detail. Varying the question each day produces a pile of interesting notes you cannot code against anything.
How to Do Diary Studies With Consumers: Step 5 — Pilot Before You Deploy
Run the whole thing end to end with two or three people who are not your target panel. Ask them to think aloud as they complete one entry. You are looking for three things: instructions they had to read twice, fields they did not know how to answer, and moments where they stopped to ask you something.
Test the technical path on the devices you expect. A photo upload that fails on a slow connection loses an entry permanently, and a reminder that arrives at 2am ends your panel.
Then revise. Cut prompts, rewrite any question that produced a shrug, and fix the consent wording where people hesitated. Two days of piloting saves a fortnight of fieldwork.
How to Do Diary Studies With Consumers: Step 6 — Run Fieldwork and Keep People Completing Entries
Review incoming entries daily, not weekly. Key Lime makes the same recommendation and adds the reason: the data volume is the real cost of the method, and daily review is what keeps it workable. Categories created in week one can be applied to week two; categories invented in week four arrive too late to be used.
Answer participant questions neutrally. If someone asks whether their answer was right, restate the prompt rather than confirming. Leading reassurance mid-study contaminates everything that follows for that participant.
When an entry is missing, send one short reminder with the due time and nothing else. Do not send a sequence of chase messages; nagging changes who completes and who does not, and the dropouts stop being random.
Drop-off is normal, usually after the first novelty, and mostly concentrated in the middle. Recover it by trimming the prompt load rather than pushing harder, checking in once mid-study with a thank-you and a reminder of what is left, and accepting thinner entries rather than policing them.
Watch for reactivity too: people behaving differently because they are being watched is a known weakness of any self-report method. A neutral, low-status framing in the briefing and no mention of what you hope to find both reduce it.
How to Do Diary Studies With Consumers: Step 7 — Code and Condense the Entries
Build one page per participant: every entry summarised, then tagged. Start with a small provisional scheme and let it grow during fieldwork, the way Zalando tagged entries as Problem, Feature Request and Decision Criteria and then filtered down to recurring patterns. That scheme is simple enough to be applied consistently and rich enough to point at decisions.
Then move from tags to patterns. Count how many participants show a behaviour, not how many times it appears. One participant describing a problem in every entry is one data point, not twenty, and the difference matters when you report.
Write per-participant summaries before you compare anyone. They expose contradiction, unusual context and the entries you would otherwise skip because they read as noise.
How to Do Diary Studies With Consumers: Step 8 — Read the Findings and Report Them
Look for what recurs across people and over the study window. A single vivid entry is a hypothesis, not a finding; three participants independently describing the same hesitation is a finding you can act on.
Triangulate rather than over-claim. A pattern from 12 people is directional evidence about behaviour and motivation, not a statistic about your market. If a survey wave can confirm how common the behaviour is, say so explicitly and keep the diary’s job as explaining how and why.
Report with quotes attached to counts: what happened, how many participants, in what situations, what it suggests, what you would change, and what you still do not know. Then name the next study.
Common Mistakes
Vague prompts. “Describe your experience” returns nothing usable. Fix: name the moment, the situation and one checkable detail.
Leading questions. “How annoying was the new packaging?” tells the panel what you want. Fix: ask what happened before asking how they felt.
Overloading participants. Ten prompts a day for fourteen days is not thorough, it is dropout. Fix: cap at three or four core prompts and honour the cap in your own reminders.
Inconsistent follow-up. Some participants get a helpful reply, others get silence, and now your sample is biased toward the confident. Fix: one standard reply template applied to everyone.
Thin consent. Consent written for text entries does not cover a photo of someone’s kitchen. Fix: separate consent lines for text, photo, audio and video, with deletion terms.
Coding everything at the end. A fortnight of entries with no tagging is an unreadable heap. Fix: 20 minutes daily, codebook updated live.
Treating 12 people as representative. This is the most common over-claim in diary reporting. Fix: state participant numbers next to every pattern and describe the panel, not the market.
Paying per piece of personal data. Fix: pay for completing the agreed study. If you pay per entry, expect length to inflate and disclosure to shrink.
Three things that consistently pay off: reviewing entries the same day they arrive, keeping one shared codebook everyone applies, and reporting patterns with counts next to the participant quotes they came from.
Frequently Asked Questions
How many participants do you need for a diary study?
Most consumer diary studies run with 12 to 15 participants, and that range is a starting point rather than a rule. For behaviour that splits into distinct cohorts (heavy users, light users, switchers), plan roughly 12 to 15 per cohort so you can compare them. Concept and message work usually wants 20 to 30 so differences are less fragile. Diary panels are small because entries are rich and longitudinal, not because they are statistically representative.
How long should a diary study run?
One to two weeks suits most consumer categories, because it captures at least two full routine cycles without fatigue setting in. Short studies, under a week, usually miss a second repetition and you cannot tell a habit from a one-off. Habitual or infrequent categories, such as appliances, car buying or banking, need four weeks or more so you catch the real decision points rather than the initial novelty.
Are paper diaries better than app or chat-based diaries?
Neither is better overall; they produce different data. Paper suits private or low-tech categories and participants who dislike phones, but adds recall delay and gives you no media or timestamps. Apps and chat channels give automatic reminders, media upload and cleaner analysis, but need setup time and a reliable phone. Decide by behaviour and panel, then pilot the technical path with two or three people before deployment.
How much should you pay participants?
Structure matters more than the headline amount. Pay a fixed amount for completing the agreed number of entries, plus any bonus for finishing on time rather than for length or personal detail. Pay nothing extra per entry, or you buy volume instead of accuracy. State the amount, the schedule and the payment method in the invitation and the consent form, and treat a shorter entry as complete data rather than a shortfall to be policed.
How do you analyse diary study data?
Review entries daily while fieldwork is open, tagging each one against a small provisional codebook that you extend as patterns appear, such as Problem, Feature Request and Decision Criteria. Write a one-page summary per participant. Then count how many participants show each behaviour rather than how many times it appears, and separate single vivid entries from patterns that recur across people and over time.
What should you ask participants to record?
Ask for six things every time so entries stay comparable: the situation, the behaviour, the thoughts behind it, the emotion, the decision point, and one detail you can check later. Add a media prompt only where it helps, such as a photo of the setting or a screenshot of a screen. Never photograph other people or account details. Keep the whole entry under two minutes so completion survives the second week.
Conclusion: What To Do First
Write the decision the study informs, on one line. Pick a logging protocol that matches the behaviour, recruit eight to ten people, and pilot two prompts with three of them. Everything else, the incentive structure, the consent wording, the daily review slot, falls into place once those four are done.
If you take one habit from this guide, take the daily one. The quality of a diary study is decided during fieldwork, entry by entry, in the twenty minutes you spend reading them while they are still fresh.
