Auteurs
Inyang I, Benke G, Morrissey J, McKenzie R, Abramson M. How well do adolescents recall use of mobile telephones? Results of a validation study. BMC Med Res Methodol. Jun 12, 2009. Ahead of print.

Background
Increased uptake of mobile phones, including among children and adolescents, has led to concerns over potential health effects, especially among young people whose developing nervous systems may be particularly vulnerable to the radiofrequency (RF) radiation emitted by mobile phone handsets and associated radio base-stations (RBS).  Most studies looking at health effects of mobile phone use have used the case-control design and have looked at brain tumours as the outcome measure.  These studies generally rely on participants’ retrospective reconstruction of mobile phone use, which is affected by recall bias and is imprecise.  A few studies have sought to validate recall of mobile phone use by adults; however participants in these validation studies were not a good representation of the underlying cohort.  There is no published study validating mobile phone use in children and adolescents.

Objective
The aim of this study was to validate mobile phone use in adolescents using software modified phones (SMP), which are ordinary mobile phones incorporating additional software to record dosimetric parameters, including number and duration of calls, within the same epidemiological cohort investigating the cognitive effects of mobile phone use in adolescents.

Methods
The validation study was carried out in within the broader Mobile Radiofrequency Phone Exposed Users Study (MoRPhEUS) – a prospective cohort study investigating cognitive effects of mobile phone use in Australian secondary school students.  For the MoRPhEUS study, 497 high school students were invited to participate, and 317 were recruited.  Participants were from 20 Melbourne secondary schools.  Invitation to participate in the validation study was extended to students who participated in the main study and who fit the inclusion criteria.  Parental socioeconomic status (SES) was assessed by residential postcode.  Self reported exposure to mobile phones was assessed using a questionnaire adapted from INTERPHONE.  Students were asked to volunteer information on use and ownership of mobile phones as well as the number and duration of calls made and received per week.  Actual phone use measured by SMPs was logged for one week and compared with self reports over the same period.

Results
Twelve schools from the initial cohort of 20 were randomly selected to participate in the validation study.  Invitations were extended to 159 students, of which 47% agreed to participate.  Fifteen of these students were subsequently excluded due to technological incompatibility, resulting in a study sample of 59 students.  Females represented 61% of participants and the mean age was 13.0 years.  Overall there was a modest correlation between self reported and actual phone use as logged by SMP based on recall of number of calls.  Agreement between SMP recorded and self reported duration of calls was poorer.  Participants whose parents belonged to a higher socioeconomic status recalled phone use better.  The authors also report the sensitivity, specificity, and positive predictive value of self-reported phone use.

Interpretation and Limitations
This study is the first to validate adolescent recall of mobile phone use and is the first to validate phone use in a sample representative of the main study.  This study supports previous findings in adults that mobile phone recall correlates better with number of calls than duration of call.  This study is limited by the potential for selection bias and by the integrity of adolescent self reports.

Conclusion
Caution should be used in interpreting results of epidemiological studies investigating health effects of mobile phone use generally, but particularly in adolescents.


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