A longitudinal research method where participants self-report their experiences, behaviors, and feelings over a period of days or weeks. Diary studies capture behavior in context over time, revealing patterns that one-time research sessions cannot.
Common contexts
- Tracking how new users build habits with a productivity app over their first 30 days
- Understanding the emotional arc of a patient using a chronic illness management tool across a treatment cycle
- Researching how a complex B2B workflow tool gets used across a full project lifecycle rather than a single session
Use when
When behavior changes over time, occurs in private contexts that researchers can't observe directly, or when you need to understand how usage patterns evolve with repeated exposure rather than first impressions.
Avoid when
Don't use a diary study when you need fast, actionable feedback — the method requires weeks of data collection and careful synthesis, making it a poor fit for sprint-cycle decisions.
Diary studies are uniquely good at surfacing the gap between what users say they do in interviews and what they actually do in practice — the most valuable entries are often the ones participants almost didn't bother writing.
Real-world examples
- Google conducted diary studies with smartphone users across multiple countries to understand real-world micro-moment behaviors, directly informing their mobile search and assistant product strategy.
- Microsoft Research used diary studies to understand how remote workers managed work-life balance during the pandemic, generating insights that shaped Microsoft Teams features.
- Procter & Gamble used longitudinal diary studies with consumers to understand laundry habits in detail, uncovering unmet needs that led to new Tide product formulations and packaging.