RT Journal Article SR Electronic T1 Validation of short term recall of mobile phone use for the Interphone study JF Occupational and Environmental Medicine JO Occup Environ Med FD BMJ Publishing Group Ltd SP 237 OP 243 DO 10.1136/oem.2004.019281 VO 63 IS 4 A1 M Vrijheid A1 E Cardis A1 B K Armstrong A1 A Auvinen A1 G Berg A1 K G Blaasaas A1 J Brown A1 M Carroll A1 A Chetrit A1 H C Christensen A1 I Deltour A1 M Feychting A1 G G Giles A1 S J Hepworth A1 M Hours A1 I Iavarone A1 C Johansen A1 L Klæboe A1 P Kurttio A1 S Lagorio A1 S Lönn A1 P A McKinney A1 L Montestrucq A1 R C Parslow A1 L Richardson A1 S Sadetzki A1 T Salminen A1 J Schüz A1 T Tynes A1 A Woodward YR 2006 UL http://oem.bmj.com/content/63/4/237.abstract AB Aim: To validate short term recall of mobile phone use within Interphone, an international collaborative case control study of tumours of the brain, acoustic nerve, and salivary glands related to mobile telephone use. Methods: Mobile phone use of 672 volunteers in 11 countries was recorded by operators or through the use of software modified phones, and compared to use recalled six months later using the Interphone study questionnaire. Agreement between recalled and actual phone use was analysed using both categorical and continuous measures of number and duration of phone calls. Results: Correlations between recalled and actual phone use were moderate to high (ranging from 0.5 to 0.8 across countries) and of the same order for number and duration of calls. The kappa statistic demonstrated fair to moderate agreement for both number and duration of calls (weighted kappa ranging from 0.20 to 0.60 across countries). On average, subjects underestimated the number of calls per month (geometric mean ratio of recalled to actual = 0.92, 95% CI 0.85 to 0.99), whereas duration of calls was overestimated (geometric mean ratio = 1.42, 95% CI 1.29 to 1.56). The ratio of recalled to actual use increased with level of use, showing underestimation in light users and overestimation in heavy users. There was substantial heterogeneity in this ratio between countries. Inter-individual variation was also large, and increased with level of use. Conclusions: Volunteer subjects recalled their recent phone use with moderate systematic error and substantial random error. This large random error can be expected to reduce the power of the Interphone study to detect an increase in risk of brain, acoustic nerve, and parotid gland tumours with increasing mobile phone use, if one exists.