title: Assessment of radiofrequency exposure from cellular telephone daily use in an epidemiological study: German Validation study of the international case-control study of cancers of the brain--INTERPHONE-Study.
abstract: OBJECTIVE
  The objective of the study is to validate self-reported cellular phone use information by comparing it with the cumulative emitted power and duration of calls measured by software-modified cellular phones (SMP). The information was obtained using a questionnaire developed for the international case-control study on the risk of the use of mobile phones in tumours of the brain or salivary gland (INTERPHONE-study).
  
  
  METHODS
  The study was conducted in Bielefeld, Germany. Volunteers were asked to use SMPs instead of their own cellular phones for a period of 1 month. The SMP recorded the power emitted by the mobile phone handset during each base station contact. Information on cellular phone use for the same time period from traffic records of the network providers and from face-to-face interviews with the participants 3 months after the SMP use was assessed. Pearson's correlation coefficients and linear regression models were used to analyse the association between information from the interview and from the SMP.
  
  
  RESULTS
  In total, 1757 personal mobile phone calls were recorded for 45 persons by SMP and traffic records. The correlation between the self-reported information about the number and the duration of calls with the cumulative power of calls was 0.50 (P<0.01) and 0.48 (P<0.01), respectively. Almost 23% of the variance of the cumulative power was explained by either the number or the cumulative duration of calls. After inclusion of possible confounding factors in the regression model, the variance increased to 26%. Minor confounding factors were "network provider", "contract form", and "cellular phone model".
  
  
  CONCLUSIONS
  The number of calls alone is a sufficient parameter to estimate the cumulative power emitted by the handset of a cellular telephone. The cumulative power emitted by these phones is only associated with number of calls but not with possible confounding factors. Using the mobile phone while driving, mainly in cities, or mainly in rural areas is not associated with the recorded cumulative power in the SMP.
authors.affiliation: Department of Epidemiology and Medical Statistics, School of Public Health, University of Bielefeld, Bielefeld, Germany. Gabriele.berg@uni-bielefeld.de
authors.forename: Gabriele
authors.initials: G
authors.lastname: Berg
authors.forename: Joachim
authors.initials: J
authors.lastname: Schüz
authors.forename: Florence
authors.initials: F
authors.lastname: Samkange-Zeeb
authors.forename: Maria
authors.initials: M
authors.lastname: Blettner
mesh_terms: D001331:Automation; D016022:Case-Control Studies; D040421:Cell Phone; D015986:Confounding Factors, Epidemiologic; D003625:Data Collection; D004781:Environmental Exposure; D005260:Female; D005858:Germany; D006801:Humans; D008297:Male; D011846:Radio Waves / Q000009:adverse effects*; D015203:Reproducibility of Results; D012984:Software; D011795:Surveys and Questionnaires; D013997:Time Factors