An international prospective cohort study of mobile phone users and health (COSMOS): Factors affecting validity of self-reported mobile phone use

•Agreement for self-reported phone use was higher for call duration than frequency.•Subjects tended to underestimate rather than overestimate mobile phone use.•Agreement for self-reported call frequency was higher in men and older subjects.•Subjects who reported symptoms were more likely to overestimate low call duration. This study investigates validity of self-reported mobile phone use in a subset of 75 993 adults from the COSMOS cohort study. Agreement between self-reported and operator-derived mobile call frequency and duration for a 3-month period was assessed using Cohen’s weighted Kappa (κ). Sensitivity and specificity of both self-reported high (≥10 calls/day or ≥4h/week) and low (≤6 calls/week or