Regression calibration of self-reported mobile phone use to optimize quantitative risk estimation in the COSMOS study

The Cohort Study of Mobile Phone Use and Health (COSMOS) study has repeatedly collected both self-reported and operator-recorded data on mobile phone use. Assessing health effects using self-reported information only is prone to measurement error, but operator data were available prospectively for only part of the study population and did not cover past mobile phone use. To optimize the available data and reduce bias, we evaluated different statistical approaches for constructing mobile phone exposure histories within COSMOS. We evaluated and compared the performance of complete case-analysis, different regression calibration methods, and multiple imputation in a simulation study with a binary health outcome. We used self-reported and operator-recorded mobile phone call data collected at baseline (2007-2012) from participants in Denmark, Finland, the Netherlands, Sweden, and the UK. Parameter estimates obtained using regression calibration methods were associated with less bias and lower mean squared error than those obtained with complete-case analysis or multiple-imputation. Our simulation study showed that regression calibration methods resulted in more accurate estimation of the relation between mobile phone use and health outcomes, by combining self-reported data with objective operator- recorded data available for a subset of the participants. ### Competing Interest Statement MF was vice chairman (2012-2020) of the International Commission on Non-Ionizing Radiation Protection, an independent body setting guidelines for non-ionizing radiation protection. She has served as advisor to a number of national and international public advisory and research steering groups concerning the potential health effects of exposure to non-ionizing radiation, currently for the World Health Organization (WHO). HK was the chair of the Committee on Electromagnetic Fields of the Health Council of The Netherlands till 2022. He currently is a member of the WHO Task Group for the Environmental Health Criteria Monograph on RF-EMF. AH is a member of the International Commission on Non-Ionizing Radiation Protection since 2020, and of the Committee on Electromagnetic Fields of the Health Council of The Netherlands, and chairs the Swedish Radiation Safety Authority's (SSM) Scientific Council on Electromagnetic Fields since 2020. AA currently is a member of the WHO Task Group for the Environmental Health Criteria Monograph on RF-EMF. MBT is currently member of the WHO groups tasked with systematic review of evidence on non-ionizing radiation and health, that is feeding into the Environmental Health Criteria Monograph on RF-EMF. All other authors declare they have no competing financial interests. ### Funding Statement The Swedish part of COSMOS has been funded by the Swedish Research Council (50096102), AFA Insurance (T-26:04), the Swedish Research Council for Health, Working Life and Welfare (2010-0082, 2014-0889), the Swedish Radiation Safety Authority (SSM2015-2408), and VINNOVA (P31735-1). VINNOVA received funds for this purpose from TeliaSonera AB, Ericsson AB and Telenor Sverige AB, to cover part of the data collection (ended 2012). The provision of funds to the COSMOS study investigators via VINNOVA was governed by agreements that guarantees COSMOS' complete scientific independence. TeliaSonera, Telenor, 3, and Tele2 made it possible for their subscribers to participate with traffic data. The UK part of COSMOS was funded for an initial 5 year period by the MTHR (Mobile Telecommunications and Health Research), an independent programme of research into mobile phones and health that was jointly supported by the UK Department of Health and the mobile telecommunications industry (project reference number 091/0006) and, subsequently, funded by the UK Department of Health via its Policy Research Programme (project reference number PR-ST-0713-00003). The UK research was also part-funded by the National Institute for Health and Care Research Health Protection Research Unit (NIHR HPRU) in Health Impact of Environmental Hazards a partnership between King's College London, Imperial College London and Public Health England (now UK Health Security Agency, UK HSA) (HPRU-2012-10141) and subsequently the NIHR HPRU in Chemical and Radiation Threats and Hazards at Imperial College London and UK HSA (grant award reference NIHR-200922). The views expressed in this publication are those of the authors and not necessarily those of the National Health service (NHS), the NIHR, the UK Department of Health or UK HSA. The Finnish cohort was supported by a grant from the National Technology Agency (TEKES), with contributions to the research programme from Nokia, TeliaSonera and Elisa; Pirkanmaa Hospital District competitive research funding (grant no. VTR 9T003); Yrjö Jahnsson Foundation (grant no. 5692); and an unrestricted grant from Mobile Manufacturers' Forum (with Pirkanmaa Hospital District as a firewall) with a contract guaranteeing the complete scientific independence of the researchers to analyse, interpret and report the results with no influence for the funding sources. The Dutch part of COSMOS was funded by the Netherlands Organisation for Health Research and Development (ZonMw) within the Electromagnetic Fields and Health Research programme (grant numbers 85200001, 85500003 and 85800001). The Danish part of COSMOS was funded by the Danish Strategic Research Council (grants 2103-05-0006/2064-04-0010). The French part of COSMOS is funded by the French Agency for Food, Environmental and Occupational Health & Safety (ANSES), project reference numbers 2013-CRD-17, 2015-CRD-30, 2018-CRD-03, 2020-CRD-RF20-01 and the International Agency for Research on Cancer. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Ethics committees reviewed and approved the study protocol in Denmark (Danish Data Protection Agency, J.nr: 2007–41–0856 and J.nr: 2005–41&–5533), Finland (Pirkanmaa Hospital District, tracking numbers R04179 and R09105), Sweden (Regional Ethical Review Board in Stockholm, 2007/1285–31/5, 2012/1608–32), and the UK (North West Haydock Research Ethics Committee, ref. 08/H1010/90). In the Netherlands, the Accredited Medical Research Ethics Committees (MRECs) assessed the protocol and found that the study did not require ethical review (protocol number 10/268C, 25/08/2010). Written or electronic informed consent to link to operator-recorded mobile phone use data was requested from each study participant. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data produced in the present study are available upon reasonable request to the authors.