Reporting reactivity in EMA appears protocol-dependent: coverage-based (120-min recall) EMA of physical activity and sedentary behavior diverged modestly from concurrent accelerometry over 7 days, whereas near-momentary (5-min) EMA showed no such divergence.
In the coverage-based (120-min recall) EMA protocol, self-reported sedentary behavior diverged linearly from accelerometry over the 7-day monitoring period.
In the coverage-based protocol, self-reported physical activity showed both linear and quadratic temporal divergence from accelerometry.
No evidence of divergence between self-reported and device-measured behavior was found in the near-momentary (5-min reporting period) protocol.
The divergence in reporting trajectories differed significantly between the coverage-based and near-momentary protocols.
The study was a secondary analysis of a US adult panel sample using concurrent accelerometry and EMA in natural environments.
The authors conclude that reporting reactivity in EMA is protocol-dependent and that coverage-based protocols show modest reactivity, challenging the assumption of reporting invariance.
Researchers often ask people to answer short smartphone surveys several times a day about what they are doing, a method called ecological momentary assessment. A worry is that answering the same questions repeatedly might change how people report, for example by making them less careful or more aware of their behavior. This study tested that concern by comparing people's survey answers about physical activity and sitting to measurements from a thigh-worn activity monitor over 7 days in 315 US adults. When surveys asked people to recall the previous 120 minutes, their reports gradually drifted away from what the monitor recorded across the week, for both sitting and physical activity. When surveys asked only about the last 5 minutes, no such drift was found, and the difference between the two survey designs was statistically significant. The drift in the longer-recall design was described as modest. This research suggests that how a survey is designed can affect whether repeated reporting stays consistent over time. It may matter for researchers who track change within a person over days or weeks, since apparent changes in self-reports could partly reflect shifts in reporting rather than real changes in behavior. The study does not say which design is better overall.
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Upload Your LabsToledo M, Schneider S, Smyth J, Junghaenel D, Stone A. (2026). Temporal Stability of Repeated Self-Reported vs Device-Measured Behavior: Observational Study Using Ecological Momentary Assessment.. Journal of medical Internet research. https://doi.org/10.2196/99953