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A growing body of evidence suggests that real‐time electronic assessments of pain are preferable to traditional paper‐and‐pencil measures. We used electronic assessment data derived from a study of patients with fibromyalgia (FM) to examine variability of pain over time and to investigate the implications of pain fluctuation in the context of a clinical trial.

The study group comprised 125 patients with FM who were enrolled in a randomized, placebo‐controlled trial of milnacipran. Pain intensity levels were captured in real time by participants using electronic diaries. Variability in pain was assessed as the standard deviation of pain entries over time (pain variability index [PVI]).

Substantial between‐subject differences in pain variability were observed (mean ± SD PVI 1.61 ± 0.656 [range 0.27–4.05]). The fluctuation in pain report was constant over time within individuals (r = 0.664, P < 0 …