Young people's perspectives of thyroid cancer screening and its harms after the nuclear accident in Fukushima Prefecture: a questionnaire survey indicating opt-out screening strategy of the thyroid examination as an ethical issue

Background

Overdiagnosis of thyroid cancer has become a major global medical issue. Ultrasound-based thyroid cancer screening has promoted overdiagnosis, and recently international recommendations state that it should not be conducted, even after a nuclear accident. The Fukushima thyroid cancer screening program was initiated in 2011 as a health policy after the nuclear accident. The risk of radiation-induced thyroid cancer was unlikely given the low radiation levels, but the thyroid cancer screening program has continued at 2-year intervals with a relatively high participation rate and is now in its fifth round. It is therefore crucial to clarify whether those targeted for screening understand the disadvantages of screening, and to identify factors that influenced their decision to participate.

Methods

We conducted an anonymous mail-based questionnaire among young people from Fukushima Prefecture (subjects) and a neighboring prefecture that was not targeted for screening (non-subjects). We asked them about the significance of the thyroid cancer screening in Fukushima Prefecture, their reasons for accepting or refusing screening, their perception of the harms of screening, and their opinions on thyroid examination at school. We compared the results of the questionnaire between subjects and non-subjects and between examinees (who were screened) and non-examinees (who declined screening).

Results

Only 16.5% of respondents were aware of the harms associated with thyroid cancer screening, with most perceiving that the benefits outweighed the harms. Comparison of subjects’ and non-subjects’ responses showed there were no significant differences between the two groups. Among subjects, there were also no differences in responses between examinees and non-examinees. The most common reason for participation in screening was that the screening was conducted in schools and perceived as obligatory.

Conclusions

These results highlighted a serious ethical issue in that school-based screening leads to making young people think that it is mandatory screening in an opt-out and default setting manner, with a lack of knowledge about the disadvantages of screening. Based on the autonomy of the subjects and the ethical principle of the post-disaster, surveys after a nuclear disaster should be conducted in an opt-in style without an opt-out style such as school-based screening.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-09341-6.

Trajectory and factors of radiation risk perception of students aged 10-12 years at the time of the Fukushima Daiichi Nuclear Power Station accident

Various studies have investigated radiation risk perceptions after the accident at the Fukushima Daiichi Nuclear Power Station. However, student surveys are limited. This study aimed to investigate the perception of radiation risk among students aged 18-20 years who were in the 5th and 6th grades of elementary school at the time of the accident. We surveyed students in the Fukushima Prefecture and outside the prefecture. Out of all the data, 59% of the respondents were living in the Fukushima Prefecture at the time of the accident and 41% outside the prefecture. Trajectory analysis showed that changes in anxiety levels over time since 2011 could be divided into five classes: (a) the anxiety was the highest, and this tendency persisted. (b) High at the beginning, but decreased more quickly than class 1. (c) High at the beginning, but it diminished quickly. (d) Not high, but did not diminish easily in later years. (e) Low from the beginning, and persisted. Multinomial logistic analysis showed that among students living outside the prefecture at the time of the accident, a significantly higher proportion was in groups 4 and 5 than in group 2. A significant proportion of boys were present in groups 3, 4 and 5. A significant proportion of students whose current educational institutions were inside the prefecture were present in group 3. The level of anxiety was associated with the academic course, but not with subjective knowledge of radiation. In contrast, in the qualitative analysis of the free text, 31% considered 'knowledge about radiation' as the reason for the reduction in anxiety level. At the time of the investigation, most young people were not anxious about radiation. However, approximately 20% still had strong anxiety. We established that continuous risk communication is necessary. Furthermore, that stabilization and support related to life in general is important.

Psychosocial support for the examinees and their families during the secondary confirmatory examination:Analyses of support records at first visit

Background and Purpose

The Thyroid Ultrasound Examination (TUE) program is conducted as part of the Fukushima Health Management Survey. Following the established criteria, examinees are called in for a secondary confirmation examination, which may induce high anxiety related to a thyroid cancer for both the examinees and their families. Therefore, Fukushima Medical University created the Thyroid Support Team to reduce anxiety. The purpose of this study is to analyze the psychosocial support for examinees and their families through two types of records, and to clarify the current issues and determine future directions of support.

Materials and methods

We analyzed 223 records of support for the first visit of examinees who attended the secondary confirmatory examination, conducted at Fukushima Medical University from September 2018 to March 2019.

Results

During the first visit, frequent topics and questions brought up by the examinees and their families were about the “Thyroid Ultrasound Examination (TUE) program” and “Examination findings”. The Thyroid Support Team members assisted them by “Responding to questions”, “Confirming the doctor’s explanation” and “Providing information”. The percentage of people with high anxiety decreased in both examinees and their family members after the examination. The level of anxiety was lower among those who had already taken the secondary confirmatory examination. Family members’ anxiety was significantly higher than that of the examinees, and anxiety levels were highly correlated between examinees and their families.

Conclusion

The psychosocial support for examinees and their families was important in reducing their anxiety. Currently there are changes in social conditions and various opinions concerning the TUE. Thus, careful explanation and the need for decision-making supports for the examinees and their families increased. Also, we should take into account the aging of the examinees and expanding the available psychosocial support.

Progress of Disaster Medicine during Ten Years after the 2011 Great East Japan Earthquake

The 2011 Great East Japan Earthquake (GEJE) has renewed the paradigm of disaster medicine. The Tohoku Journal of Experimental Medicine (TJEM) widened its scope to include the disaster science from the health perspectives. TJEM has been accumulating 76 articles related with "disaster" or "pandemic" out of which 69 were published after 2011. Tohoku University established the International Research Institute of Disaster Science (IRIDeS) that took initiative to impact the Sendai Framework for Disaster Risk Reduction 2015-2030 (Sendai Framework) to include health aspect. Sendai Framework provided the platform for collaboration of different sectors, including the terminology that defines the concept of disaster, risk, hazard & exposure, vulnerability and coping capacity. Disaster medicine covers the diverse causes and damages of disasters by various hazards in this globalized and rapidly changing world. TJEM articles range the physical and mental health damage after the GEJE and other disasters with approved ethical consideration of investigations from the view point of affected area, mechanisms of hazard to affect human health including the radiation, virus or hazardous materials, proposal of refinement of health system to cope with disasters such as mental health support, risk communication, disaster medical coordination and hospital business continuity plan and future perspectives with reconstruction including Tohoku Medical Megabank Project. TJEM scope on disaster medicine had been widened during the 10 years after GEJE and IRIDeS can be the bridging hub not only between the health sector and other sectors, but also between disaster medicine and other medical disciplines.

Lessons learned from Chernobyl and Fukushima on thyroid cancer screening and recommendations in case of a future nuclear accident

Exposure of the thyroid gland to ionizing radiation at a young age is the main recognized risk factor for differentiated thyroid cancer. After the Chernobyl and Fukushima nuclear accidents, thyroid cancer screening was implemented mainly for children, leading to case over-diagnosis as seen in South Korea after the implementation of opportunistic screening (where subjects are recruited at healthcare sites). The aim of cancer screening is to reduce morbidity and mortality, but screening can also cause negative effects on health (with unnecessary treatment if over-diagnosis) and on quality of life. This paper from the SHAMISEN special issue (Nuclear Emergency Situations - Improvement of Medical And Health Surveillance) presents the principles of cancer screening, the lessons learned from thyroid cancer screening, as well as the knowledge on thyroid cancer incidence after exposure to iodine-131. The SHAMISEN Consortium recommends to envisage systematic health screening after a nuclear accident, only when appropriately justified, i.e. ensuring that screening will do more good than harm. Based on the experience of the Fukushima screening, the consortium does not recommend mass or population-based thyroid cancer screening, as the negative psychological and physical effects are likely to outweigh any possible benefit in affected populations; thyroid health monitoring should however be made available to persons who request it (regardless of whether they are at increased risk or not), accompanied with appropriate information and support.

The Association between Utilization of Media Information and Current Health Anxiety Among the Fukushima Daiichi Nuclear Disaster Evacuees

The 2011 nuclear disaster in Fukushima was not only a health disaster, but also an information disaster. Although media can promote health communication following disasters, studies have revealed associations between media information and negative psychological reactions. To clarify the relationship between media utilization and current health anxiety due to radiation exposure, a cross-sectional questionnaire survey was conducted in Fukushima. We selected 2000 subjects from evacuation (i.e., 500) and non-evacuation (i.e., 1500) areas by two-stage stratified random sampling. As the independent variable, participants were asked about current health anxiety due to radiation exposure at the time of answering the questionnaire. For utilization of media about radiation exposure, local media, national media, Internet media, public broadcasts, and public relations information from local government were set as the dependent variables. Questionnaire data were analyzed by evacuation type (i.e., forced/voluntary). In a multivariate logistic regression analysis, the use of public relations information was significantly associated with lower anxiety for the forced evacuees (odds ratio: 0.72; 95% confidence interval: 0.56–0.93). Our findings highlight the importance of public relations information from local government in terms of it being associated with lower current health anxiety, and this could potentially aid in preparing for future disasters.

Association of Anxiety over Radiation Exposure and Acquisition of Knowledge Regarding Occupational Health Management in Operation Leader Candidates of Radioactivity Decontamination Workers in Fukushima, Japan: A Cross-Sectional Study

An operation leader (OL) of radioactivity decontamination workers is required by law to have accurate knowledge of occupational health management (OHM) such as working environment management, control of operations, and health management as a field supervisor in Japan. The purpose of the current study is to examine the association between anxiety over radiation exposure and the possession/acquisition of the OHM knowledge required for OLs. In this cross-sectional study, data were collected before and after training sessions held by Fukushima Prefecture Labor Standard Associations in Fukushima, Japan, in 2017. Eighty-seven males who completed the questionnaires were enrolled to this study. As a result, acquisition of knowledge of working environment management was significantly associated with an increase of anxiety over radiation exposure after the session comparing the situation before and after the session (knowledge possession; odds ratio = 4.489; 95% confidence interval = 1.216, 16.571). In conclusion, acquisition of accurate knowledge of how to manage working environment management was associated with anxiety over radiation exposure. Although acquisition of said knowledge may contribute to the reduction of physical health risks, it may increase mental health risks. Both mental health support for OLs with accurate knowledge and educational support for those without accurate knowledge are required.

Modeling reconstruction-related behavior and evaluation of influences of major information sources

Reconstruction has progressed steadily since the 2011 TEPCO's Fukushima Daiichi Nuclear Power Station accident. However, some people still hesitate to eat foods from Fukushima or to travel there, and there are concerns about the health risks of radiation. We investigated the relationships among reconstruction-related behavior, risk perception, types of information, and information sources, in order to consider appropriate measures for providing information and promoting reconstruction-related behavior a number of years after the accident. We conducted an online questionnaire survey (n = 1000) of Tokyo residents. First, a factor analysis was conducted on knowledge associated with radiation. Two factors were extracted; namely, "physical knowledge" and "health/social knowledge." We conducted structural equation modeling to construct a model of "knowledge," "radiation risk perception," and "intention concerning reconstruction-related behavior." "Intention concerning reconstruction-related behavior" decreased with "radiation risk perception" and increased with "health/social knowledge." In addition, "health/social knowledge" negatively affected "radiation risk perception;" this effect was not large, but it was significant. Second, respondents were clarified by information sources using a cluster analysis. Clusters that included respondents who got information from public relations materials issued by municipalities and websites of administrative agencies had a higher factor score for "health/social knowledge" than other clusters. The cluster of respondents who did not get any particular knowledge had the lowest factor score, which was significant, and also had a low "perception of reconstruction."

The association between socioeconomic status and reactions to radiation exposure: a cross-sectional study after the Fukushima Daiichi nuclear power station accident

Risk perception and individual reactions to risk are not necessarily comparable, and socioeconomic status may affect individual reactions to risk. This study aimed to investigate the association between socioeconomic status and reactions to radiation exposure risk. This cross-sectional study, based on a self-reported online survey was conducted between 3 March and 21 March 2012, one year after the accident at Fukushima Daiichi nuclear power station. We used feelings of anxiety and risk-averse behavior concerning radiation exposure as dependent variables, and equivalent income and educational attainment as independent variables. Multiple logistic regression analysis was applied to estimate adjusted odds ratios (aORs) and 95% confidence intervals (95% CIs) with adjustment for possible confounders. Among 10 000 participants, 23.0% felt anxious and 12.0% engaged in risk-averse behavior for radiation exposure. Participants with a higher socioeconomic status tended not to feel anxious but undertook risk-averse behavior. Participants in the highest quartile income category did not report feeling anxious but showed prevalent undertaking of risk-averse behavior for radiation exposure compared to the lowest income category (for anxiety, aOR, 0.77; 95% CI, 0.64–0.93, for risk-averse behavior, aOR, 1.33; 95% CI, 1.04–1.69). University or graduate-school graduates were associated with greater risk-averse behavior compared to junior high school or high school graduates (aOR, 1.49; 95% CI, 1.29–1.73). Socioeconomic status may affect reactions to radiation exposure risk. Risk communication strategies should consider the socioeconomic status of those affected.

Mental Health Recovery of Evacuees and Residents from the Fukushima Daiichi Nuclear Power Plant Accident after Seven Years-Contribution of Social Network and a Desirable Lifestyle

The 2011 Fukushima nuclear accident resulted in the exposure to radiation and evacuation, which has created psychological distress among the Fukushima residents. With the provision of multi-faceted support and the progress of the reconstruction, their mental health has appeared to show signs of recovery. However, there have been few studies investigating their recovery. To clarify the related factors associated with mental health recovery, a cross-sectional questionnaire survey was conducted. Subjects whose answers were associated with Resilience, Recovery, and Remitting patterns of mental health status were categorized in the Recovery group, while those associated with Delayed/Chronic dysfunction were placed in the Non-recovered group. In a multivariable logistic regression analysis, disaster-related unemployment (odds ratio (OR): 0.80, 95% CI (confidence interval): 0.65–0.99) and economic hardship (OR: 0.80, 95% CI: 0.65–0.98) were associated with the hindrance of recovery. In contrast, overall good health (OR: 1.47, 95% CI: 1.20–1.80), regular physical activity (OR: 1.23, 95% CI: 1.01–1.50), social interaction with friends (OR: 1.25, 95% CI: 1.00–1.55), and established social roles (OR: 1.44, 95% CI: 1.14–1.82) were associated with the promotion of recovery. In conclusion, our study showed a positive association between mental health recovery and a desirable lifestyle and social network, particularly with social roles. Thus, the provision of active social roles can promote recovery related to a disaster as with multi-faceted support.

Effect of Radiological Countermeasures on Subjective Well-Being and Radiation Anxiety after the 2011 Disaster: The Fukushima Health Management Survey

After the Fukushima Daiichi Nuclear Power Station accident in 2011, concerns about radiation exposure and decline in subjective well-being have been reported. To tackle these problems, various countermeasures in relation to radiation have been implemented. In this study, we comprehensively evaluated the effects of radiological countermeasures on subjective well-being (e.g., satisfaction with life (SWL) and emotional well-being) and radiation anxiety, through a questionnaire survey targeting Fukushima residents (N = 1023). Propensity scores matching was applied to evaluate significant effects of radiological countermeasures on subjective well-being and radiation anxiety. Among the radiological countermeasures, thyroid examination, whole body counter, and air dose monitoring showed the highest proportions of participation, utilization, and useful evaluation, suggesting a high degree of public attention focused on these countermeasures. The basic survey was associated with significant increases in SWL and self-rated health (SH). Thyroid examination was significantly associated with not only a reduction in radiation anxiety but also an increase of emotional stress, suggesting the importance of careful design of system and detailed communication. Food inspection was associated with deterioration in SH. Those who utilized explanatory meetings showed increases in sadness, worry, and radiation anxiety, indicating that additional attention is required of the experts and authorities involved in explanatory meetings.

Presenting information on regulation values improves the public's sense of safety: Perceived mercury risk in fish and shellfish and its effects on consumption intention

Risk communication aims to promote health and understanding through information exchange; however, explanations regarding the basis of regulation values for the public are insufficient. Moreover, it is unclear how information presentation affects the public’s sense of safety and their consumption intentions. We first investigated the relationship between perception of mercury-risk in fish and shellfish and individual attributes and knowledge. We then examined how presenting information on regulation values and primary factors regarding perception affected sense of safety toward regulations and food-consumption intentions. An online survey was conducted with Japanese individuals (N = 1148). Respondents were randomly assigned to one of three groups based on the presentation level of regulation values. People who frequently consumed tuna had a high perception of dread risk of mercury. This suggests that the dread risk perception of mercury does not determine tuna-type consumption behavior; rather, individuals’ consumption behavior determines dread risk perception of mercury. Among those with high tuna-type consumption, those receiving information that a safety factor of 10 times had been considered showed a significantly greater sense of safety than did the group that was not presented with information on regulation values (odds ratio (95% confidence interval): 2.04 (1.18–3.53), p < 0.05). However, presentation of regulation values showed a weak but significantly positive correlation with excessive intake of tuna-type fish (odds ratio: 2.95 (0.93–9.32), p < 0.10). Presenting the information on regulation values increases sense of safety; however, it may also lead to excessive intake.

Risk Perception and Anxiety Regarding Radiation after the 2011 Fukushima Nuclear Power Plant Accident: A Systematic Qualitative Review

The purpose of this study was to provide a review of the publications of the risk perceptions or anxiety regarding radiation among people living in Japan after the 2011 Fukushima nuclear power plant accident. Two database (MEDLINE and PsycINFO) and hand-searched the references in identified publications were searched. For each identified publication, the measurements and time related-change of risk perception and anxiety regarding radiation were summarized. Twenty-four publications were identified. Quantitative measures of risk perception or anxiety were roughly divided into two types: single-item Likert scales that measure anxiety about radiation; and theoretical, or model-based measures. Rates of Fukushima residents with radiation-related anxiety decreased from 2012 to 2015. Factors governing risk perception or radiation-related anxiety were summarized by demographics, disaster-related stressors, trusted information, and radiation-related variables. The effects of risk perception or anxiety regarding radiation were summarized as severe distress, intention to leave employment or not to return home, or other dimensions. This review provides summary of current findings on risk perception or anxiety regarding radiation in Japan after the accident. Further researches are needed about detailed statistical analysis for time-related change and causality among variables.

Additional risk of diabetes exceeds the increased risk of cancer caused by radiation exposure after the Fukushima disaster

The 2011 Fukushima disaster led to increases in multiple risks (e.g., lifestyle diseases and radiation exposure) and fear among the public. Here, we assessed the additional risks of cancer caused by radiation and diabetes related to the disaster and the cost-effectiveness of countermeasures against these conditions. Our study included residents of the cities of Minamisoma and Soma (10-40 km and 35-50 km north of the Fukushima Daiichi (N° 1) Nuclear Power Station, respectively). We used the loss of life expectancy (LLE) as an indicator to compare risks between radiation exposure and diabetes. We also estimated the cost-effectiveness of radiation-related countermeasures, including restricted food distribution, decontamination, and whole-body counter tests and interventions. Metformin therapy was selected as a representative management for diabetes. The diabetes-related LLEs among residents were 4.1 (95% confidence interval: 1.4-6.8) ×10-2 years for the whole population and 8.0 (2.7-13.2) ×10-2 years for 40s to 70s in a scenario that considered the additional incidence of diabetes during the first 10 years. The cancer-related LLEs caused by lifetime exposure to radiation were 0.69 (2.5-97.5 percentile: 0.61-0.79) ×10-2 years for the whole population and 0.24 (0.20-0.29) ×10-2 years for 40s to 70s. The diabetes-related LLEs among residents in the above-mentioned scenario were 5.9-fold and 33-fold higher than those attributed to average radiation among the whole population and among the 40s to 70s age groups, respectively. The costs per life-years saved of the radiation countermeasures (i.e., restricted food distribution, decontamination, and whole-body counter tests and interventions) were >1 to >4 orders of magnitude higher than those of general heath checkups and conventional management for diabetes. Our findings indicate that countermeasures to mitigate diabetes are warranted. Policy-makers' and individuals' understanding of multiple risks after any disaster will be essential to saving the lives of victims.

Towards a Long-Term Strategy for Voluntary-Based Internal Radiation Contamination Monitoring: A Population-Level Analysis of Monitoring Prevalence and Factors Associated with Monitoring Participation Behavior in Fukushima, Japan

Following Japan’s 2011 Fukushima nuclear incident, we assessed voluntary-based monitoring behavior in Minamisoma City—located 10–40 km from the Fukushima nuclear plant—to inform future monitoring strategies. The monitoring in Minamisoma included occasional free of charge internal-radiation-exposure measurements. Out of around 70,000 individuals residing in the city before the incident, a total of 45,788 residents (female: 52.1%) aged ≥21 were evaluated. The monitoring prevalence in 2011–2012 was only 30.2%, and this decreased to 17.9% in 2013–2014. Regression analyses were performed to estimate factors associated with the monitoring prevalence and participation behavior. The results show that, in comparison with the age cohort of 21–30 years, the cohort of 71–80 and ≥81 years demonstrated significantly lower monitoring prevalence; female residents had higher monitoring prevalence than male residents; those who were living in evacuation zones at the time of the incident had higher monitoring prevalence than those who lived outside any of the evacuation zones; for those living outside Fukushima and neighboring Prefectures post-incident monitoring prevalence decreased significantly in 2013–2014. Our findings inform the discussion on the concepts of radiation risk perception and accessibility to monitoring and societal decision-making regarding the maintenance of the monitoring program with low monitoring prevalence. We also stress the possibility that the monitoring can work both to check that internal contamination levels are within acceptable limits, and as a risk communication tool, alleviating individuals’ concern and anxiety over radiation contamination.

Communicating With Residents About Risks Following the Fukushima Nuclear Accident

The Fukushima nuclear accident in March 2011 posed major threats to public health. In response, medical professionals have tried to communicate the risks to residents. To investigate forms of risk communication and to share lessons learned, we reviewed medical professionals’ activities in Fukushima Prefecture from the prefectural level to the individual level: public communication through Fukushima Health Management Surveys, a Yorozu (“general”) health consultation project, communications of radiological conditions and health promotion in Iitate and Kawauchi villages, dialogues based on whole-body counter, and science communications through online media. The activities generally started with radiation risks, mainly through group-based discussions, but gradually shifted to face-to-face communications to address comprehensive health risks to individuals and well-being. The activities were intended to support residents’ decisions and to promote public health in a participatory manner. This article highlights the need for a systematic evaluation of ongoing risk communication practices, and a wider application of successful approaches for Fukushima recovery and for better preparedness for future disasters.

Evaluating Risk Communication After the Fukushima Disaster Based on Nudge Theory

Using nudge theory and some examples of risk communication that followed the Fukushima disaster, this article discusses the influences and justifications of risk communication, in addition to how risk communication systems are designed. To assist people in making decisions based on their own value systems, we provide three suggestions, keeping in mind that people can be influenced (ie, “nudged”) depending on how risk communication takes place: (1) accumulate knowledge on the process of evaluating how the method of risk communication and a system’s default design could impact people; (2) clarify the purpose and outcomes of risk communication; and (3) see what risk communication might be ethically unjustifiable. Quantitative studies on risk communication and collective narratives will provide some ideas for how to design better risk communication systems and to help people make decisions. Furthermore, we have shown examples of unjustifiable risk communication.

Psychosocial Issues Related to Thyroid Examination After a Radiation Disaster

A thyroid ultrasound examination program has been conducted in the aftermath of the Fukushima Daiichi Nuclear Power Plant accident to address concerns about the increased risk of thyroid cancer similar to those experienced by local residents after the 1986 Chernobyl accident. This is the second-largest thyroid cancer screening in younger age ever, following only that conducted after Chernobyl. As the natural history of thyroid cancer in younger populations is not well characterized, large-scale screening using thyroid ultrasound could result in overdiagnosis, even with careful planning, as has been experienced in South Korea. Awareness regarding the thyroid gland is generally low among residents, who tend to directly associate examination results with radiation exposure and are likely to develop newfound anxiety and feelings of self-condemnation and guilt. We reviewed the dilemma surrounding cancer screening and particularly underscored the need to address psychosocial issues associated with possible overdiagnosis. We modified our approach to address individual and social anxiety induced by results of screening conducted after the Fukushima accident. These findings and our experiences regarding the psychosocial issues related to thyroid examination should assist residents in their lifelong decision making and help them prepare for future disasters.

Evaluation of Risk Perception and Risk-Comparison Information Regarding Dietary Radionuclides after the 2011 Fukushima Nuclear Power Plant Accident

In the wake of the 2011 Fukushima Daiichi Nuclear Power Station accident, to facilitate evidence-based risk communication we need to understand radiation risk perception and the effectiveness of risk-comparison information. We measured and characterized perceptions of dread risks and unknown risks regarding dietary radionuclides in residents of Fukushima, Tokyo, and Osaka to identify the primary factors among location, evacuation experience, gender, age, employment status, absence/presence of spouse, children and grandchildren, educational background, humanities/science courses, smoking habits, and various types of trustworthy information sources. We then evaluated the effects of these factors and risk-comparison information on multiple outcomes, including subjective and objective understanding, perceived magnitude of risk, perceived accuracy of information, backlash against information, and risk acceptance. We also assessed how risk-comparison information affected these multiple outcomes for people with high risk perception. Online questionnaires were completed by people (n = 9249) aged from 20 to 69 years in the three prefectures approximately 5 years after the accident. We gave each participant one of 15 combinations of numerical risk data and risk-comparison information, including information on standards, smoking-associated risk, and cancer risk, in accordance with Covello’s guidelines. Dread-risk perception among Fukushima residents with no experience of evacuation was much lower than that in Osaka residents, whereas evacuees had strikingly higher dread-risk perception, irrespective of whether their evacuation had been compulsory or voluntary. We identified location (distance from the nuclear power station), evacuation experience, and trust of central government as primary factors. Location (including evacuation experience) and trust of central government were significantly associated with the multiple outcomes above. Only information on “cancer risk from radiation and smoking risk” enhanced both subjective and objective understanding without diminishing trust in all participants and in the high dread-risk perception group; use of other risk-comparison information could lead the public to overestimate risk.