Best practice transfer by public health nurses in Japan: actual conditions and related factors.

BACKGROUND: The workload of public health nurses (PHNs) working for local governments has been increasing as health issues become more diverse and complicated. Even amidst the ongoing administrative and fiscal reforms, there is an urgent need to ensure how effectively and efficiently public health nurses can practice in health service development. The objective of this research was to clarify the actual conditions of best practice transfer (BPT) and its related factors. METHODS: An anonymous postal and self-administered questionnaire survey was conducted among PHNs working at 334 sites, including the local government offices and health centers across Japan, and analysed mainly through logistic regression analysis. RESULTS: One hundred eighty-five of the 334 institutions (55.4%) agreed to participate, and of the 966 questionnaire forms distributed, 709 forms (73.4%) were collected, of which 702 responses (72.7%) were valid. Although less than half (43.2%) have experience in BPT in health service development, more than 80% are willing to perform going forward. Significant factors for both the group with experience in BPT and the group with willingness to perform include an organizational culture that promotes BPT, as well as multiple elements of the workplace environment and facilitating factors related to knowledge and learning. The experienced group recognised the needs for criteria to evaluate the adaptability of best practice, while the willing group, to evaluate the quality of practice. CONCLUSIONS: Through a nationwide survey, this research elucidated for the first time the actual conditions of BPT by PHNs in Japan and related factors. The results indicated the importance of developing a system to promote BPT at the workplace level, also highlighted the importance for practitioners and experts, including researchers, to work together to develop practical guidelines to ensure evidence-based practices. Urgent actions are needed for the national and local governments to develop a system to promote BPT from diverse perspectives, building on the findings of this research.

Implementation Degree Assessment Sheet for Health Program in Japan by Customizing CFIR: Development and Validation.

PURPOSE: More than 70% of public health nurses in Japan belong to government agencies, and there is a need for further evidence-based capacity development for program implementation. The purpose of this research was to develop an Implementation Degree Assessment Sheet (IDAS) by customizing the Consolidated Framework for Implementation Research (CFIR) to health programs in Japan. METHODS: The draft IDAS (five domains, 31 constructs) created by customizing the CFIR was refined by the researchers and modified through pre-testing. The survey covered full-time public health nurses (PHNs) affiliated to all prefectures and the cities with health centers of Japan. The survey was conducted as an anonymous, self-administered questionnaire survey by mail. RESULTS: One hundred eighty-five of the 334 institutions (55.4%) agreed to participate in our survey. Of the 966 questionnaire forms distributed, 709 forms (73.4%) were collected, of which 702 responses (72.7%) were valid. No item required consideration of deletion based on the results of item analysis, and our confirmatory factor analysis on model fitness between the five IDAS domains and CFIR showed sufficient fit indices after modification. With regard to reliability, Cronbach's coefficient alpha, a measure of internal consistency, stayed above 0.8 overall. Our verification of stability with the split-half (odd/even) method resulted in a Spearman-Brown reliability coefficient of 0.95. The correlation coefficient between the IDAS scores and the research utilization competency score, used as an external criterion, was 0.51 (p<0.001), supporting the coexistence validity of the criterion-related validity of the IDAS. The significant differences were observed between known-groups, supporting the known-group validity of the IDAS. CONCLUSION: This study developed the IDAS and confirmed constant reliability and validity. Hereafter, it is necessary to promote the required capacity development based on the actual degree of implementation in order to use the IDAS for the competency development of public health nurses and related professions to deliver health programs.

Prevalence of and factors associated with smoking among Japanese medical students.

BACKGROUND: The aim of the present study was to determine the prevalence of and factors associated with smoking among Japanese medical students, to help promote effective antismoking measures in this population. METHODS: From the 80 university medical schools in Japan, 20 were randomly selected and invited to participate in our survey. The survey focused on medical students and employed an anonymous self-administered questionnaire. Information on each university's antismoking measures was obtained using a separate questionnaire administered to teaching staff. The survey was conducted from December 2006 through March 2007. Factors associated with smoking were identified by using the chi-square test and multiple logistic regression analysis. RESULTS: A total of 1619 valid surveys were returned. The overall prevalence of smoking was 13.7% (18.1% among men and 5.1% among women). Factors associated with smoking among medical students were male sex, enrollment at a private medical university, smoking by siblings, alcohol consumption, coffee consumption, insomnia, and less than 6 hours of sleep per night. CONCLUSIONS: Antismoking education must be further promoted to Japanese medical students, with consideration given to the factors associated with smoking behavior found in the present study.

[Factors associated with willingness to undergo vaccination against haemophilus influenzae type B (Hib)].

OBJECTIVES: The purpose of this study was to examine factors that affect the willingness to undergo Hib vaccination and to pay (WTP) for it. METHODS: The subjects of the survey were 1,185 parents with infants attending nursery schools in Machida city, Tokyo. A total of 46.3% returned the completed questionnaire, which covered information about Hib willingness to undergo vaccination, their WTP for it, and components of the health belief model (HBM). RESULT: Approximately half (50.3%) of the respondents were willing to have vaccination. The mean WTP was 2581 JPY, and approximately 80% of those who stated their WTP were willing to pay 3000 JPY or less. Perceived susceptibility, severity, and benefits were positively correlated with the willingness to have vaccination and the WTP, while perceived economic barriers were negatively correlated. Also, WTP was positively correlated with income. CONCLUSION: In order to promote the Hib vaccination program, it is necessary to provide information based on the HBM, especially information that affects the perception of benefits of vaccination, and to take measures to reduce the level of out-of-pocket payment, considering households who have lower incomes.

Alcohol consumption behavior of pregnant women in Japan.

OBJECTIVE: This study was conducted to clarify the prevalence of alcohol consumption among pregnant women in Japan and its associated factors. METHOD: 344 institutions participated in the survey which was conducted in February 2006. Each subject was requested to fill out a self-administered anonymous questionnaire. Factors associated with alcohol consumption during pregnancy were examined using the chi-squared test and logistic regression analysis. RESULTS: The number of effective responses was 18,965. The prevalence of alcohol consumption before the confirmation of pregnancy and during pregnancy was 44.6% and 4.6% respectively. The following items were recognized as being associated with promoting alcohol consumption during pregnancy: greater number of weeks of pregnancy, more pregnancies, fewer years of schooling, being employed, an alcohol consumption before the confirmation of pregnancy, smoking during pregnancy, ignorance about the effects of alcohol consumption on fetuses, receiving advice regarding alcohol abstention, difficulty maintaining sleep, and daytime sleepiness. CONCLUSION: It is important to have a more comprehensive understanding of the factors associated with the alcohol consumption behavior of pregnant women, as revealed in the present study, in order to develop future policies for preventing alcohol consumption among pregnant women.

Alcohol consumption and abstention among pregnant Japanese women.

BACKGROUND: In order to clarify the alcohol consumption status of pregnant women in Japan and the characteristics of pregnant women who abstained from alcohol after their pregnancy had been confirmed, a nationwide questionnaire-based study of alcohol consumption behavior was performed. We also examined the factors associated with alcohol consumption during pregnancy and abstention after the confirmation of pregnancy. METHODS: After random sampling, 260 institutions participated in the survey; these were selected from a list of survey points fixed by the Japan Association of Obstetricians and Gynecologists. The study was conducted on pregnant women with confirmed pregnancies by using self-administered anonymous questionnaires during the period from February 1 through 14, 2002. RESULTS: Alcohol consumption during pregnancy was reported in 11.1% of the study participants, and abstention after the confirmation of pregnancy, in 76.9%. Significant associations were recognized between higher education and both alcohol consumption during pregnancy and abstention after pregnancy confirmation. Furthermore, alcohol consumption was significantly associated with parity, smoking, and shorter sleep duration, whereas abstention was significantly associated with less frequent alcohol consumption and knowledge regarding the risk of alcohol consumption. CONCLUSION: The results clarified the factors associated with alcohol consumption during pregnancy and abstention after the confirmation of pregnancy in Japan.

Is passive smoking associated with sleep disturbance among pregnant women?

STUDY OBJECTIVE: Pregnant women suffer from sleep disturbance, which may be aggravated by passive smoking. In this study we investigated the effects of passive smoking on sleep disturbance during pregnancy. DESIGN: Two cross-sectional questionnaire surveys conducted in 2002 and 2006. SETTING: Clinical institutions specializing in obstetrics and gynecology that participated in the nationwide surveys: 260 in the 2002 survey and 344 in the 2006 survey. PARTICIPANTS: 16,396 and 19,386 pregnant women in Japan surveyed in 2002 and 2006, respectively. INTERVENTION: N/A. MEASUREMENTS AND RESULTS: Pregnant women exposed to passive smoking were likely to have sleep disturbances, such as subjective insufficient sleep, difficulty in initiating sleep, short sleep duration, and snoring loudly/breathing uncomfortably. Smoking pregnant women had the same sleep disturbances and also experienced excessive daytime sleepiness and early morning awakening. The prevalence of 5 types of sleep disturbance (insufficient sleep, difficulty in initiating sleep, short sleep duration, excessive daytime sleepiness, and snoring loudly/breathing uncomfortably) among nonsmokers with environmental tobacco smoke showed a mean value intermediate between that of active smokers and that of nonsmokers without environmental tobacco smoke. CONCLUSION: Passive smoking is independently associated with increased sleep disturbance during pregnancy.

Use of alcohol and hypnotic medication as aids to sleep among the Japanese general population.

OBJECTIVE: The present study was conducted to clarify the prevalence of the use of alcohol and hypnotic medication as sleep aids, and associated factors, in the general population in Japan. METHODS: The survey was conducted in June 2000, using self-administered questionnaires, targeting a population that was selected randomly from among 300 communities throughout Japan. A total of 18,205 responses indicating alcohol use and 16,804 responses indicating hypnotic medication use were analyzed. RESULTS: The prevalence of alcohol use as a sleep aid one or more times per week was 48.3% among men and 18.3% among women. The prevalence of the use of hypnotic medication one or more times per week was 4.3% among men and 5.9% among women. The prevalence of alcohol used as a sleep aid increased gradually for men and women up to age 55-59 years and 40-44 years, respectively, and then declined with increasing age thereafter. The prevalence of the use of hypnotic medication among both men and women showed a trend toward a gradual increase with age. The use of alcohol as a sleep aid was associated with "difficulty maintaining sleep," but no such problem was associated with the use of hypnotic medication. CONCLUSIONS: Alcohol is a more popular sleep aid than hypnotic medication. The factors associated with the use of alcohol and of hypnotic medication are different.

The relationship between depression and sleep disturbances: a Japanese nationwide general population survey.

OBJECTIVE: Among the existing epidemiologic studies that have examined the relationship between depression and sleep disturbances, there are few nationwide studies that have been conducted on subjects representing the general population. The present study was therefore conducted to clarify the relationship between depression and sleep disturbances, in particular the relationship between depression and both sleep duration and subjective sleep sufficiency, using a large sample representative of the general population. METHOD: The survey was conducted in June 2000, using self-administered questionnaires, targeting a population that was selected randomly from among 300 communities throughout Japan. Among the respondents, data from 24,686 individuals aged 20 years or older were analyzed. The Center for Epidemiologic Studies Depression Scale was used to assess the presence of depression. Sleep status, including sleep duration, subjective sleep sufficiency, and the presence or absence of insomnia symptoms, was evaluated. RESULTS: Those whose sleep duration was less than 6 hours and those whose sleep duration was 8 hours or more tended to be more depressed than those whose sleep duration was between 6 and 8 hours. Thus, sleep duration exhibited a U-shaped association with symptoms of depression. As subjective sleep sufficiency decreased, symptoms of depression increased, indicating a linear inverse-proportional relationship. CONCLUSION: The fact that sleep duration and subjective sleep sufficiency exhibited different relationships with symptoms of depression indicates that these 2 sleep parameters each have their own significance with regard to depression. These findings may be useful in the medical management of mental diseases.

Competence necessary for Japanese public health center directors in responding to public health emergencies.

OBJECTIVE: To clarify the "competencies" required of public health center directors in "public health emergency responses." METHODS: We selected as our subjects six major public health emergencies in Japan that accorded with a definition of a "health crisis." Their types were: (1) natural disaster; (2) exposure to toxic substances caused by individuals; (3) food poisoning; and (4) accidental hospital infection. Item analysis was conducted using the Incident Analysis Method, based on the "Medical SAFER Technique." RESULTS: The competencies of public health center directors required the following actions: (1) to estimate the impact on local health from the "first notification" of the occurrence and the "initial investigation"; (2) to manage a thorough investigation of causes; (3) to manage organizations undertaking countermeasures; (4) to promptly provide precise information on countermeasures, etc.; and (5) to create systems enabling effective application of countermeasures against recurrence of incidents, and to achieve social consensus. CONCLUSION: For public health preparedness, public health center directors should have the following competencies: (1) the ability to estimate the "impact" of public health emergencies that have occurred or may occur; (2) be able to establish and carry out proactive policies; (3) be persuasive; and (4) have organizational management skills.

[Study on actual situation of community industrial physicians for small and medium-sized enterprises and their involvement in community occupational health services].

The subjects of this study were 405 Japan Medical Association authorized industrial physicians, Community Industrial Physicians (CIPs), who belonged to the Shinjuku, Nakano, and Suginami Words' regional medical associations in the jurisdiction of the Shinjuku Labor Standards Inspection Office. Between November and December, 2003, the CIPs were mailed a questionnaire requesting information about their affiliations and activities, and as indicators of their willingness to participate in Community Occupational Health Services, they were asked about the pros and cons of having their names published as Industrial Physicians, and/or practitioners for Regional Occupational Health Centers, or Regular Health Checks. 152 replies were received, effective response rate of 37.5%, and among these 94 replies were from CIPs who work as part-time industrial physician. Overall, CIPs attend Community Occupational Health Services (COHS) voluntarily, and wish to participate in them more in the future. CIPs who work as part-time industrial physician have knowledge of working safety and hygiene and are providing advice and guidance on working conditions and environments. Also, they are well informed about support services for small and medium-sized enterprises which is thought to be connected with their willingness to participate in COHS. Furthermore, it is important that part-time CIPs activities are appreciated by their respective place of work.

The prevalence of restless legs syndrome among pregnant women in Japan and the relationship between restless legs syndrome and sleep problems.

STUDY OBJECTIVES: To clarify the prevalence of restless legs syndrome (RLS) in pregnant women living in Japan and to analyze the relationship between sleep problems and RLS, in order to discuss ways for pregnant women to obtain comfortable sleep and to improve the health of both the mother and child. DESIGN: A cross-sectional questionnaire survey. SETTING: 500 clinical institutions with maternity services were randomly sampled from a list of organizations identified in a survey by the Japan Association of Obstetricians and Gynecologists. Of these 500 institutions, 260 participated in the survey. PARTICIPANTS: 16,528 pregnant women living in Japan. INTERVENTIONS: N/A. MEASUREMENTS AND RESULTS: In this survey of pregnant women, the prevalence of RLS was found to be 19.9%. An analysis was conducted on the relationship between RLS and other factors such as subjective evaluation of sleep, difficulty initiating sleep, difficulty maintaining sleep, early morning awaking, and excessive daytime sleepiness. The result of this analysis suggested that women with these sleep-related problems were more likely to have RLS than those without. In addition, RLS was more prevalent in the later stages of pregnancy. CONCLUSION: In the pregnant women in our survey, the prevalence of RLS was found to be 19.9%, which is higher than the prevalence of RLS that has been found in the general public in a previous study. This suggests that RLS-related sleep problems may be an important public health issue among pregnant women in Japan. This finding may have implications for attempts to improve sleep hygiene in this group.

[Cost-benefit analysis of community based rehabilitation program using willingness to pay measured by the contingent valuation method].

OBJECTIVE: There have been few studies on economic evaluation of publicly provided community health services in Japan. The purpose of the present investigation was to conduct a cost-benefit analysis of a community based rehabilitation program provided by municipalities, using the willingness to pay (WTP) measured by the contingent valuation method, a survey-based approach to measure the monetary valuation for the benefit. METHODS: The study was held in 18 wards of Yokohama city. The cost per capita of the program in each ward was calculated using the data from a statement of accounts and a report of activities of public health nurses, other officials, and volunteers, in the 1999 fiscal year. The WTP for the program was measured by a survey of 631 people who participated in the programs held in October and November, 2000. The mean, median, and 95% CI of WTP were calculated as measures of the benefit. RESULTS: The response rate of the survey was 73.4%. The mean and median WTP were yen 441 and yen 300 respectively, and the 95% CI ranged from yen 800 to yen 1,682. The WTP was negatively related to the duration of functional disability, and positively related to income. However, the WTP was not significantly related to self-perceived effectiveness of the program and the SF-36. The costs per capita without the cost of volunteers among 18 wards ranged from yen 2,079 to yen 6,732, and those with the cost of volunteers ranged from yen 3,289 to yen 8,366. The net benefit per capita was negative. CONCLUSIONS: To conduct cost-benefit analyses of community based rehabilitation programs more precisely, it is necessary to measure the costs of medical care and long term care saved and the benefits to others (e.g. volunteers, community residents, etc.) and to assess the WTP so that various aspects of effectiveness (health and non-health benefits) are taken into account.

[Correlated factors for activities of health related crisis management of Prefectural public health centers and municipalities in Japan].

OBJECTIVE: To clarify correlated factors with activities of health related crisis management (HRCM) by prefectural public health centers (PPHCs) and municipalities. METHODS: A cross-sectional study of 460 PPHCs and 3,173 municipalities was performed with questionnaires mailed directly to the institutions. Activities of HRCM, which included 24 hour shifts according to the magnitude of the crisis, health services for sufferers, sanitary improvement of shelters, information services for the public, and simulation to cope with health related crises, were evaluated. Items other than simulation were assessed with four grade scales and simulation by whether it was carried out. Correlated factors, which included the size of population, whether a health related crisis had happened in the last 5 years and whether there were facilities that could be a cause of such crises. RESULTS: The response rates of PPHCs and municipalities were 72.8% and 61.7% respectively. More than 60% of PPHCs had good activity for 24 hour shifts for crises of great magnitude. However less than 50% of PPHCs and municipalities performed well with health services for sufferers, sanitary improvement of shelters and information services for the public. Moreover less than 20% of PPHCs and municipalities implemented simulations. Population correlated with health services for sufferers in both municipalities and PPHCs and with sanitary improvement in PPHCs, although the coefficients were small. Municipalities in which a health related crisis had occurred in the past and those in which there were facilities that could be a cause of health related crises performed better activities than others. This was not the case for PPHCs. CONCLUSION: The study indicated that neither PPHCs nor municipalities performed activities of HRCM sufficiently. It is suggested that PPHCs need to support municipalities, which have no experience of public health emergencies and which have an environment with no obvious danger.

[Changes in community health and welfare services with introduction of the long-term care insurance system in Japan].

OBJECTIVE: In Japan, a long-term care insurance system for elderly people was introduced in April, 2000. We have conducted a survey using a questionnaire in order to explore consequent changes in community health and welfare services. METHODS: We sent questionnaires to all municipal governments (671 cities, 1,991 towns, 567 villages and 23 wards) in Japan in November, 2001, and obtained replies from 441 cities (response rate: 65.7%), 800 towns (40.2%), 197 villages (34.9%), and 16 wards (69.6%). The questionnaire included questions concerning the budget and manpower for community health and welfare services, the state of the long term care insurance system, and the activities of public health nurses. RESULTS: A total of 57% of all municipal governments was found to be carrying out the long term care insurance program in collaboration with other governments. In order to clarify the changes in welfare services for elderly people from the budgetary viewpoint, we calculated the ratios of the 2000 and 2001 fiscal budgets applied for welfare services for elderly people, in comparison with the 1999 fiscal year. The budgets for elderly people declined to about 40% in 2000 and 2001 compared with 1999, since the budget for care services was transferred to the account of the long term care insurance system. The activities of public health nurses employed by municipal governments were not affected by the introduction of long term care insurance system. About 80% of all municipal governments suggested that both the amounts of care services received by each elderly people and the number of elderly people who received care services were increasing, and about 70% indicated that the quality of care services was improved with introduction of the long term care insurance system. DISCUSSION: Most municipal governments consider that introduction of the long term care insurance system has had a good influence on community health and welfare services. Moreover, our results suggest that the long term care insurance has a beneficial impact on care services themselves.

[An epidemiological study of sleep problems among the Japanese pregnant women].

OBJECTIVE: The objective of the study was to identify: 1) what kinds of sleep problems that pregnant women experience in Japan; and 2) the relationships between sleep problems and month of pregnancy, sleep problems and the number of pregnancies, and sleeping hours, by means of a questionnaire given to pregnant women in Japan. Conditions to assure good quality sleep were studied. METHODS: Of 500 obstetric facilities which were randomly selected from areas surveyed by the Japan Association of Obstetricians and Gynecologists, 260 finally agreed to participate in this study. Women who had their pregnancy confirmed and were on a revisit to the 260 obstetric facilities were enrolled. These pregnant women completed anonymous self-administered questionnaires during the waiting time for treatment and submitted them to the obstetric facilities in sealed envelopes. The questionnaire covered personal attributes such as age and highest level of education, pregnancy status, working status, and patterns of smoking and alcohol drinking. Sleep-related items such as 1) subjective sleep quality, 2) difficulty in getting to sleep, 3) frequent awakenings, 4) waking up too early, 5) sleeping hours and 6) daytime drowsiness were also included. RESULTS: The month of pregnancy was significantly related to four sleep-related items, including difficulty in getting to sleep and waking up too early. With respect to the relationship between the number of pregnancies and sleep problems, significance was found for five sleep-related items, including subjective sleep quality and waking up too early. Poor subjective sleep quality was significantly related to sleeping less than seven hours and whether or not pregnant women had a regular job. It was also suggested that the greater the number of pregnancies, the shorter the sleeping hours. When responses to each sleep-related item were compared between pregnant women and the general population, the former were more likely to have sleep problems. CONCLUSION: These findings suggest that as well as the number of pregnancies and month of pregnancy with sleeping hours may be factor intimately related to sleep problems during pregnancy. A good quality sleep during pregnancy is vital for normal maternal health and fetal growth and sufficient sleeping hours are therefore needed. Attention should therefore be paid to the finding that pregnant women were more likely to have sleep problems than the general population.

Prevalence of smoking and associated factors among pregnant women in Japan.

OBJECTIVE: This study was conducted to estimate the prevalence of smoking among pregnant women living in Japan and to analyze the factors associated with their smoking behavior. METHOD: Five hundred institutions with maternity services were randomly sampled from a list of the Japan Association of Obstetricians and Gynecologists. Of these institutions, 260 participated in the survey which was conducted in February 2002. Using a self-reported anonymous questionnaire, a survey on smoking behavior, drinking behavior and sleep status was conducted on pregnant women. Chi-square tests and logistic regression analyses were used to examine the factors associated with their smoking behavior. RESULTS: Data were obtained from a total of 16,414 pregnant women. The prevalence of smoking during pregnancy was 9.9% [95% confidence interval (CI) 9.4%, 10.4%]. The quit rate of smoking among pregnant woman was 61.9% [95% CI 60.4%, 63.4%]. The odds ratios for smoking during pregnancy were significantly higher in women with relatively young age, less schooling, multiparous, exposure to passive smoking, short sleep duration and in women who drank. CONCLUSION: Smoking among pregnant women remains an important public health problem in Japan. It is necessary to promote antismoking measures based on the results of this study.

Epidemiological study on passive smoking among Japanese infants and smoking behavior of their respective parents: a nationwide cross-sectional survey.

BACKGROUND: Passive smoking is a well-known health hazard for infants. This study was conducted to: (1) estimate the prevalence of passive smoking among Japanese infants and (2) clarify the prevalence of indoor smoking and associating factors among parents having infants. METHODS: Subjects were all 53,575 infants born throughout Japan on January 10-17, 2001 or July 10-17, 2001. When the infants reached 6 months of age, the questionnaires were mailed to the homes. Family members answered questions that included information about the current smoking behavior of the parents. RESULTS: A total of 44,562 questionnaires (83.2%) were analyzed. The prevalence of smoking among the mothers and the fathers were 17.1% and 63.5%. The percentages of mothers and fathers who smoked indoors were 12.1% and 36.2%. The percentage of households where mothers and/or fathers smoked indoors was 37.5%. Multivariate logistic analysis indicated that young age, having a spouse who was a smoker, infants having many siblings, the mother not breast-feeding, and lower annual incomes had significantly higher odds ratios for both the mother's and the father's indoor smoking. CONCLUSIONS: Passive smoking is common among Japanese infants. To protect Japanese infants from passive smoking, further public health measures must be taken.

Influences of the absence of random assignment of bids on estimating willingness to pay using a discrete-choice question.

This study examined the influences of the interaction between a bid and the respondent's characteristics due to insufficient random assignment of bids on the estimation of willingness to pay (WTP) using data from a discrete-choice question. A contingent valuation survey of 152 examinees undergoing X-ray testing for gastric cancer screening was conducted, and the median and mean WTP for the serum pepsinogen test were estimated using a logistic regression model to which the interaction terms between the bid and the respondent's characteristics, which included gender, age, annual income, frequency of prior use of a gastric cancer screening program, and perceived health, were added. There were remarkable differences in the estimated WTP according to whether the interaction term of annual income, to which the bids had failed to be assigned randomly and which had been positively correlated with the bid, was added in the model. It is suggested that it may be necessary to check if the bids were randomly assigned to the respondent's characteristics and, when correlations with the bid are found, to adjust their interaction effects.