title: An evaluation of self-reported mobile phone use compared to billing records among a group of engineers and scientists.
abstract: Most epidemiologic studies of potential health impacts of mobile phones rely on self-reported information, which can lead to exposure misclassification. We compared self-reported questionnaire data among 60 participants, and phone billing records over a 3-year period (2002-2004). Phone usage information was compared by the calculation of the mean and median number of calls and duration of use, as well as correlation coefficients and associated P-values. Average call duration from self-reports was slightly lower than billing records (2.1 min vs. 2.8 min, P = 0.01). Participants reported a higher number of average daily calls than billing records (7.9 vs. 4.1, P = 0.002). Correlation coefficients for average minutes per day of mobile phone use and average number of calls per day were relatively high (R = 0.71 and 0.69, respectively, P < 0.001). Information reported at the monthly level tended to be more accurate than estimates of weekly or daily use. Our findings of modest correlations between self-reported mobile phone usage and billing records and substantial variability in recall are consistent with previous studies. However, the direction of over- and under-reporting was not consistent with previous research. We did not observe increased variability over longer periods of recall or a pattern of lower accuracy among older age groups compared with younger groups. Study limitations included a relatively small sample size, low participation rates, and potential limited generalizability. The variability within studies and non-uniformity across studies indicates that estimation of the frequency and duration of phone use by questionnaires should be supplemented with subscriber records whenever practical.
authors.affiliation: Exponent, Inc., Menlo Park, California, USA.
authors.forename: Mona
authors.initials: M
authors.lastname: Shum
authors.forename: Michael A
authors.initials: MA
authors.lastname: Kelsh
authors.forename: Asher R
authors.initials: AR
authors.lastname: Sheppard
authors.forename: Ke
authors.initials: K
authors.lastname: Zhao
mesh_terms: D000328:Adult; D017677:Age Distribution; D040421:Cell Phone / Q000191:economics* / Q000706:statistics & numerical data*; D003365:Costs and Cost Analysis; D004738:Engineering; D005260:Female; D006801:Humans; D008297:Male; D011939:Mental Recall; D008875:Middle Aged; D011846:Radio Waves / Q000009:adverse effects; D011996:Records; D015203:Reproducibility of Results; D012108:Research Personnel; D012586:Science; D057566:Self Report; D017678:Sex Distribution; D011795:Surveys and Questionnaires; D013997:Time Factors