External dose estimation in an early stage after the Fukushima Daiichi Nuclear Power Plant accident. Lessons learned from behavior surveys using self-administered questionnaires

The Basic survey as a part of the Fukushima Health Management Survey was a self-administered questionnaire that asked subjects to record and send back information on their behavior in the 4 months after the Fukushima disaster. These behavior records were then digitalized, and individual estimates of external radiation exposure were made using daily ambient dose rate maps. Several issues arose in the process from receiving the completed questionnaires, estimating doses, and informing residents of the results. After sending out the questionnaires, a large number (8,000 responses per day at its peak) were returned over a short period, and these needed to be processed. To aid this, the number of staff involved in digitalizing the hand-written questionnaires was greatly expanded. Another issue was how to increase the response rate. While actions taken to raise the response rate did increase the number of responses to some extent, the response rate of the prefecture overall did not increase greatly. Such problems may be encountered in large-scale behavior surveys should another disaster occur in the future. This report gives an overview of these problems and how they were dealt with, which will provide a resource for public dose assessments should another disaster occur in the future. (author)