From Population Averages to Individual Realities: A Debate on Using Intensive Longitudinal Methods in Mental Health Nursing Research

Accessible Summary Originality This debate essay introduces intensive longitudinal methods (ILMs), including daily diary methods, experience sampling methodology, ecological momentary assessment, and ambulatory assessment to psychiatric‐mental health nurses. It contrasts ILMs with conventional cross‐sectional and retrospective designs by showing how frequent, repeated measurements in everyday environments can reveal how psychiatric symptoms fluctuate and interact with contextual factors in real time. Significance ILMs support patient‐centred care and recovery‐oriented mental health care by generating individual‐level data that reflect each person's unique symptom patterns, triggers, and trajectories rather than relying only on population averages. Findings from ILM studies can inform more tailored nursing assessments and interventions—for example, distinguishing whether a patient's mood is more affected by sleep, social contact, or daily stressors—and support shared decision‐making between nurses and patients. ILMs can be practically embedded into clinical practice through smartphones, web applications, and wearable devices, with emerging opportunities to combine these methods with artificial intelligence for enhanced monitoring, early risk detection and care planning. Rigour The essay draws upon foundational textbooks and recent peer‐reviewed studies of ILMs to ensure that its methodical overview is based in established and up‐to‐date evidence. It discusses key methodological considerations, such as participant burden, missing data management, identification of confounders, and the need for measures that are sensitive to within‐person change and provides practical guidance for psychiatric‐mental health nursing researchers planning to use ILMs.