Validating self-reported mobile phone use in adults using a newly developed smartphone application
Geertje Goedhart, Hans Kromhout, Joe Wiiart, Roel Vermeulen. Validating self-reported mobile phone use in adults using a newly developed smartphone application. Occupational and Environmental Medicine. Published Online First 26 August 2015.
What this paper adds
- How much weight is given to the findings of epidemiological studies on health effects from mobile phone use depends to a large extent on how well these studies can account for inaccuracies in their exposure assessment, that is, self-reported mobile phone use.
- A newly developed smartphone application was used to record actual mobile phone use, enabling validation of self-reported phone use. In addition to the frequency and duration of phone calls, laterality, use of hands-free devices and data transfer were recorded by the application.
- Consistent with previous observations among adults, duration of calls was on average overestimated, while the number of calls was underestimated.
- Laterality data recorded by the application suggested that there is considerable within-person variability at the side of the head the phone is used, and in the percentage of call time the phone was actually near the head during voice calls.
- The observed recall errors and precision of reported laterality and hands-free use can be used to quantify and improve radiofrequency exposure models based on self-reported mobile phone use.
Several studies have been performed to validate recall of mobile phone use among adults, by comparing with operator records, or by using hardware-modified or software-modified phones (HMP, SMP).2 ,6–9 The use of operator records is, however, often limited by incomplete records (eg, no information on incoming calls), or the inability to correct for shared phone users, prepaid users or business-phone users.2 Moreover, these validation studies did not collect data on laterality and/or the use of hands-free devices, two important determinants of RF dose in the brain, used in studies on brain tumour risk. A potential risk from RF is expected to exist primarily on the side of the head where the phone is usually held (ipsilateral exposure) and, to a lesser extent, at the opposite side of the head (contralateral exposure).10 ,11 Whether people can accurately recall the side of the head they generally held their phone is yet unknown. Furthermore, no information is available on the percentage of call time that people use hands-free devices (ie, lower exposure to the brain).
... The Q1 and Q3 questionnaires were based on the mobile phone part of the questionnaire developed and used within the MOBI-Kids study, a multinational case–control study investigating the potential effects of childhood and adolescent exposure to electromagnetic fields from mobile communications technologies on brain tumour risk.12
The app is currently also used within the multinational Mobi-Expo study, a validation study on self-reported mobile phone use among young people, as part of the MOBI-Kids study.13
In total, 6869 calls were monitored by the app. Per week, the participants made on average (SD) 16.1 (14.4) calls, spoke on the phone for 47.5 (56.1) minutes, sent and received 12.4 (10.2) text messages and transferred 435.6 (902.1) MB ....The average call duration per week was significantly higher among participants aged 25 to 34 (p=0.05) and 45 to 54 (p<0 .01="" 2g="" among="" and="" br="" carried="" compared="" data="" females="" group="" males="" mostly="" nbsp="" networks.="" oldest="" out="" p="0.04)." rather="" than="" the="" to="" transfer="" via="" was="" wi-fi="" years="">
On average, participants held the phone for 86% of the total call time near the head. Participants who reported using the phone generally on the right side of their head did use it on average for 70.7% of the total call time on the right side versus 16.3% on the left side (table 3). Self-reported left-side users held the phone more on the left (66.2%) than the right (18.8%) side of their head. The few participants who reported using the phone on both sides of the head actually used it more on the right (52.2%) than the left (32.2%) side. For an averaged 14% of the total call time, the phone was not held near the head, because of hands-free device usage (headset: 2.9%, speaker mode: 5%, Bluetooth: 2.7%), or because of other actions that required holding the phone away from the head (3.4%). Three (5.4%), 19 (33.9%) and 11 (19.6%) participants reported having used a headset, the speaker mode of the phone or a Bluetooth headset/car kit, respectively (table 4). The percentage of recorded hands-free device usage increased with the increasing reported frequency of using hands-free devices, although numbers were small especially in the highest frequency categories.
We observed that participants on average underestimated the number of calls they made and received by a ratio of 0.65 (self-report to recorded), while they overestimated the duration of calls by a ratio of 1.11. The direction of underestimation/overestimation is consistent with most previous validation studies among adults; however, these studies reported higher ratios for both the number (ranging from 0.77 to 0.91) and duration (ranging from 1.39 to 1.45) of calls.7–9
An important finding was the significant impact of the level of phone use on the recall, that is, participants with a higher level of reported phone use were more likely to overestimate their number and duration of calls, while underestimation was more likely among participants who reported lower levels of use. The same trend was observed in the INTERPHONE study.8 ,9 This has important implications for epidemiological studies on mobile phone use, as it will most likely lead to an underestimation of the risk, if any, for adverse health outcomes. RF dose models based on the recalled number and duration of calls should therefore account for differential recall errors by level of phone use.
... we observed that the report of the current number and duration of calls at baseline (0 months) was not better than the recall after 6 months, although the baseline report and recall were covering different but consecutive time periods. This implies that people find it difficult to make an estimation of their mobile phone use, independent of time interval (at least within a 6-month time period). [My note: This suggests that prospective cohort studies (e.g., COSMOS) face the same exposure assessment problems as retrospective case-control studies (e.g. Interphone).
In conclusion, we used a smartphone app to record actual phone use, which had several advantages over previously used operator records, SMPs or HMPs for the validation of self-reported mobile phone use. Besides the recall error observed for the number and duration of calls, this was the first study that was able to explore the actual percentage of total call time that participants held their mobile phone close to the head, and the actual percentage of hands-free device usage. Our findings have implications for epidemiological studies exploring the possible health effects of RF emissions from mobile phones, in which the exposure assessment is based on people's recall.
Goedhart G, Vrijheid M, Wiart J, Hours M, Kromhout H, Cardis E, Eastman Langer C, de Llobet Viladoms P, Massardier-Pilonchery A, Vermeulen R.
Using software-modified smartphones to validate self-reported mobile phone use in young people: A pilot study. Bioelectromagnetics. 2015 Jul 30. doi: 10.1002/bem.21931. [Epub ahead of print]
A newly developed smartphone application was piloted to characterize and validate mobile phone use in young people. Twenty-six volunteers (mean age 17.3 years) from France, Spain, and the Netherlands used a software-modified smartphone for 4 weeks; the application installed on the phone recorded number and duration of calls, data use, laterality, hands-free device usage, and communication system used for both voice calls and data transfer. Upon returning the phone, participants estimated their mobile phone use during those 4 weeks via an interviewer-administered questionnaire. Results indicated that participants on average underestimated the number of calls they made, while they overestimated total call duration. Participants held the phone for about 90% of total call time near the head, mainly on the side of the head they reported as dominant. Some limitations were encountered when comparing reported and recorded data use and speaker use. When applied in a larger sample, information recorded by the smartphone application will be very useful to improve radiofrequency (RF) exposure modeling from mobile phones to be used in epidemiological research.
Per week, the participants made on average 19 calls (standard deviation [SD]=13.2), spoke on the phone for 30.4 min (SD=28.8), and transferred 329.6 megabytes (MB) (SD=320.6) of data (Table 1).
... average number of calls and call duration increased statistically significantly with increasing age ...
... Participants from France had, on average, a higher number and duration of calls than participants from Spain and NL,
Spearman correlation coefficients between SMSP-recorded and self-reported number and duration of calls and data use were 0.75, 0.77, and 0.59, respectively (Fig. 3). On average, participants seemed to underestimate number of calls made and received (geometric mean ratio of self-reported to SMSP-recorded = 0.65, 95% confidence interval (CI) 0.50–0.85). SMSP-recorded calls, however, also included unsuccessful outgoing calls (i.e., no connection); when excluding outgoing calls of 0–2 s (potentially unsuccessful calls, n=120), the geometric mean ratio increased to 0.68, 95%CI 0.53–0.89. Total call duration was on average overestimated by participants (geometric mean ratio =1.71, 95%CI 1.28–2.30).
While an overestimation of call duration was consistently observed in previous validation studies, both over- and underestimations of number of calls have been observed [Parslow et al., 2003; Samkange-Zeeb et al., 2004; Vrijheid et al., 2006a, 2009; Inyang et al., 2009; Aydin et al., 2011b].
Laterality measurements from a larger sample are required to estimate a more realistic exposure to both sides of the head.
Joel M. Moskowitz, Ph.D., Director
Center for Family and Community Health
School of Public Health
University of California, Berkeley
Electromagnetic Radiation Safety
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