JMIR Publications

ABSTRACT

Background:

A central concern in Ecological Momentary Assessment (EMA) research is whether repeated self-report alters the reporting process itself. In most EMA domains, longitudinal stability of reporting is assumed but rarely tested.

Objective:

This study leveraged concurrent accelerometry as a temporal anchor to evaluate (1) whether self-reported physical activity (PA) and sedentary behavior (SB) exhibited temporal shift across a 7-day monitoring period and (2) if this temporal shift differs across near-Momentary (5-minute reporting period) and Coverage-based (120-minute recall period) EMA protocols.

Methods:

We conducted a secondary analysis of 315 US adults recruited from the Understanding America Study panel between January and July 2023 for the current study. Participants were monitored in their natural environments for 7 days via two measurement methods: continuous thigh-worn activPAL4 accelerometry and five daily smartphone EMA prompts assessing PA and SB. Reporting reactivity was defined as divergence in the temporal trajectories of EMA-reported behavior relative to accelerometry. Multilevel models with random intercepts and slopes tested if linear and quadratic Study Day effects differed across the two methods (Method×Study Day interactions). Protocol differences were examined using multivariable Method×Protocol×Study Day interactions comparing Coverage-based and near-Momentary EMA designs.

Results:

In the Coverage protocol, EMA-reported PA and SB exhibited temporal trajectories that diverged significantly from concurrent accelerometry (SB linear divergence: b = 1.40, 95% CI 0.20 to 2.61, p = .022; PA linear divergence: b = -1.91, 95% CI -2.93 to -0.90, p < .001; PA quadratic divergence: b = 0.28, 95% CI 0.12 to 0.44, p < .001). No evidence of such divergence was found in the near-Momentary protocol. The divergence in reporting trajectories differed significantly between the two protocols (SB linear 3-way interaction: b = -2.58, p = .015; PA linear 3-way interaction: b = 1.86, p = .040).

Conclusions:

Reporting reactivity in EMA appears protocol-dependent. The Coverage protocol was associated with modest reporting reactivity, which challenges the common assumption of reporting invariance in EMA and underscores the importance of considering protocol design when interpreting within-person change.