2024 年 2 巻 1 号 p. 1-11
Objective: This study evaluated the effect of eHealth literacy on increasing the ratio of human papillomavirus vaccinations among Japanese university students. Methods: A Cross-sectional study was conducted from April 27th to May 10th in 2023. A self-reporting questionnaire was used, including variables of age, faculty & department belonging at a university, the human papillomavirus vaccination frequency, the human papillomavirus vaccination request status, knowledge of cervical cancer, knowledge of the human papillomavirus vaccine, and eHealth Literacy. Results: The study subjects were 441 with a mean age of 19.59 ± 1.40 years old. The effect of the motivation to get the HPV vaccination was analyzed using a multivariable logistic regression analysis using a forward stepwise selection method (Likelihood Ratio). Five factors out of 13 were chosen as the decided factors. Knowing the vaccine type and injection spot of the vaccination was significantly associated with the motivation to get the HPV vaccination (OR = 4.650, 95%CI: 3.291–6.572, p < 0.001). Having the proper knowledge of the side effects of HPV vaccination was also significantly associated with the motivation to get the HPV vaccination (OR = 2.624, 95%CI: 1.807–3.811, p < 0.001). A low level of eHealth Literacy was also significantly negatively associated with motivation (OR = 0.522, 95%CI: 0.302–0.901, p = 0.02).
Conclusions: The finding that eHealth literacy affects the motivation to get the human papillomavirus vaccination can help people who work in the health, medical, and educational fields to make a strategy to spread the correct information about the human papillomavirus vaccination to the specific target population.
Dr. Zur Hausen of the University of Heidelberg in Germany 1983 introduced the human papillomavirus (HPV)1). Vaccines against HPV have been available since 2006 and recommended by the World Health Organization (WHO) since 20092,3). In 2016, it was estimated that HPV immunization programs targeted only 12% of young adolescent females worldwide, and only 6% of girls aged 10–20 had vaccination by the end of 20144). The WHO Cervical Cancer Elimination strategy includes coverage targets for scale-up by 2030 of HPV vaccination to 90% of all adolescent girls, twice-lifetime cervical screening to 70%, and treatment of pre-invasive lesions and invasive cancer to 90%5).
In Japan, vaccination against HPV had been approved for use in October 2009. It is known that the infectious cases of HPV are higher in low- and middle-income countries; however, the cases of infection and death rate are increasing in Japan6). One of the reasons is Japan’s Ministry of Health, Labor, and Welfare (MHLW) announced the suspension of its recommendation for routine HPV immunization for about eight years from 2013 to 2021. The government decision was affirmed based on the side effects that happened after the vaccinations, and only 0.3% to 3.3% of young females between 11 years old and 14 years old who became between 18 years old and 22 years old in 2023 had the vaccinations during the time7,8). In November 2021, it was confirmed that the effectiveness of HPV vaccination was more than the side effects8). The Japanese government recommended resuming HPV vaccination in April 20229). The HPV vaccination voucher had been sent to people called the “catch-up generation” who had been born between April 2nd, 1997, and April 1st, 2007, and missed the opportunity of HPV vaccination due to the government decision. However, those people’s vaccination rate is lower than other generations. It might be happening because of a wrong impression or image from the past. In Japan, the repeated broadcast of adverse events, which are regarded as functional disorders, has discouraged many individuals from getting their daughters vaccinated10–12), and that must affect the rate of immunizations of HPV vaccination. It also depended on how much knowledge those targeted people had about HPV vaccination13). It is essential to make people regain their trust in medicine by addressing their concerns and determining effective methods for providing the correct information regarding HPV vaccination.
The younger generation uses the internet often and earns knowledge from it. However, it does not mean they consistently earn the correct information if they do not have high eHealth literacy. eHealth literacy14,15) highlights the need to examine the different contexts where health information is obtained and used to address health literacy16). Norman & Skinner defined eHealth literacy as the ability to appraise health information from electronic sources and apply the knowledge gained to addressing or solving a health problem14). It may be a new intervention strategy to provide correct information about HPV vaccination online if we can determine the relationship between accurate information regarding HPV vaccination and eHealth literacy in this study. The Japanese version of the eHealth Literacy Scale was already provided by Mitsutake et al., so we will use it in this study17).
In our study, we would like to discuss the relationship between the correct information regarding HPV vaccination and eHealth literacy. Therefore, this study evaluated the effect of eHealth literacy on increasing the ratio of HPV vaccination in female Japanese university students.
This study recruited 474 female university students from April 27th to May 10th in 2023. Thirty-three data were excluded from the study because part of their data was missing. The study subjects were 441 with a mean age of 19.59 ± 1.40years. Informed consent was obtained from all subjects by the Helsinki Declaration. The Okayama University Graduate School of Health Sciences, Ethics Committee approved this study (#OUHS2023-0009F).
Study DesignA cross-sectional study was conducted.
A self-reporting questionnaire was used, including variables of age, faculty & department belonging at a university, HPV vaccination frequency, HPV vaccination request status, knowledge of cervical cancer, knowledge of HPV vaccine, and eHealth Literacy. The eHealth Literacy was measured by using the eHealth Literacy Scale (eHEALS). The eHEALS is an 8-item measure of eHealth literacy developed to measure consumers’ combined knowledge, comfort, and perceived skills at finding, evaluating, and applying electronic health information to health problems. It was designed by Norman & Skinner. Cronbach’s alpha value was 0.88, and Construct validity was also measured and proved15). The Japanese version was developed by Mitsutake et al. Cronbach’s alpha value was 0.93, and test-retest reliability was r = 0.6317). We used the eHEALS score of 23 points as a median to divide participants into two groups. The participants in the high-value group had more than 23 points of eHEALS, and the low-value group had less than 23 points of eHEALS.
Statistical AnalysesPearson’s chi-squared test was used to confirm the relationship between the eHEALS and HPV vaccination frequency, the knowledge of HPV vaccine/cervical cancer.
Multivariable logistic regression analysis by forward stepwise selection method (Likelihood Ratio) was used to determine the obstructive factors towards the HPV vaccination.
P values of <0.05 were considered to indicate statistical significance.
Pearson’s chi-squared test was performed using the EZR (Easy R) software program (version 1.61 for Windows; https://www.jichi.ac.jp/saitama-sct/SaitamaHP.files/statmedEN.html)20).
Multivariable logistic regression analysis was performed using the IBM SPSS 23.0 software program (version 23.0 for Windows; IBM Corp., Armonk, NY, USA).
The subjects’ characteristics are listed in Table 1.
| n (%) | |||
|---|---|---|---|
| Faculty & department | Faculty of Medicine | Department of Medicine | 13 (2.9) |
| Department of Health Sciences (Nursing/Radiological Technology/ Medical Laboratory Science) | 304 (68.9) | ||
| Faculty of Education | Teacher’s License course | 39 (8.8) | |
| School Nurse Teacher’s course | 11 (2.5) | ||
| Other Faculties | Department of Human Studies | 10 (2.3) | |
| Program for Global Learners | 2 (0.5) | ||
| Department of Law | 6 (1.4) | ||
| Department of Agriculture | 7 (1.6) | ||
| Department of Science | 3 (0.7) | ||
| Department of Earth Sciences | 5 (1.1) | ||
| Department of Engineering | 17 (3.9) | ||
| Faculty of Pharmaceutical Sciences/Division of Pharmacy (6 years) | 8 (1.8) | ||
| Faculty of Pharmaceutical Sciences/Division of Pharmaceutical Sciences (4 years) | 3 (0.7) | ||
| Dental School | 13 (2.9) | ||
| HPV vaccination frequency | Once/Twice/Complete (Three times) | 183 (41.5) | |
| Never | 258 (58.5) | ||
| HPV vaccination request status | Continuing vaccination | 135 (30.6) | |
| Undecided | 154 (34.9) | ||
| Never | 42 (9.5) | ||
| Completed the vaccination | 110 (24.9) | ||
| eHEALS | Classification | High-value group | 224 (50.8) |
| Low-value group | 217 (49.2) | ||
| The average number of eHEALS score | 22.9 points/40 |
The subjects belonging to the Department of Health Sciences enrolled in this study most because we only accepted female participants based on the purpose of this study. The other answers to the questionnaire such as HPV vaccination frequency, HPV vaccination request, Classification of eHealth, and The average number of eHEALS scores were almost balanced (Table 1).
We also asked participants about the HPV vaccination request status and divided it into two reasons. One was the positive reasons for continuing vaccination (Table 2). It was the most compelling reason to know the effect of vaccination for continuing vaccination. Free vouchers and the recommendation from family members were also practical reasons. On the other hand, the negative reasons for unwanted vaccination were also answered (Table 3). It was the most compelling reason to worry about the side effects of vaccination for unwanted vaccination. If participants feel that getting vaccinated is bothersome, it also leads them to avoid getting vaccinated. Family members’ ideas also influenced them not to get vaccinated.
| The positive reasons for continuing vaccination | n (%) |
|---|---|
| Knowing the effect of vaccination | 193 (35.9) |
| Free voucher | 124 (23.0) |
| Recommendations from family members | 112 (20.8) |
| Knowing the safety of vaccination | 61 (11.3) |
| Recommendations from someone besides family members | 44 (8.2) |
| Others | 4 (0.7) |
| The negative reasons for unwanted vaccination | n (%) |
|---|---|
| Worry about the side-effects of vaccination | 122 (34.9) |
| Bothersome | 59 (16.9) |
| Family members are against the idea of vaccination | 43 (12.3) |
| People around me haven’t gotten the vaccination, either | 37 (10.6) |
| Lack of knowledge of vaccination | 28 (8.0) |
| Missing free voucher | 21 (6.0) |
| Pain | 20 (5.7) |
| Others | 11 (3.1) |
| Unnecessary | 7 (2.0) |
| Someone, besides family members, are against the idea of vaccination | 2 (0.6) |
We examined the relationship between the eHEALS and HPV vaccination frequency and the knowledge of HPV vaccine/cervical cancer by using a Pearson’s chi-squared test. The results of this analysis are displayed in Table 4. Participants in the high-value group of eHEALS knew the reason for the past suspension of the HPV vaccine more significantly than the participants in the low-value group of eHEALS (χ2(1) = 15.005, p < 0.001). Participants in the high-value group of eHEALS supported the statement that the HPV vaccine is effective in preventing cervical more significantly than the participants in the low-vale group of eHEALS (χ2(3) = 18.458, p < 0.001). Participants in the high-value eHEALS knew that HPV vaccination prevents cervical cancer more significantly than the participants in the low-value group of eHEALS (χ2(2) = 14.973, p = 0.001). Participants in the high-value eHEALS knew the cervical cancer threat more significantly than the participants in the low-value group of eHEALS (χ2(3) = 14.190, p = 0.003). Participants in the high-value eHEALS knew the vaccine type and injection spot of the vaccination more significantly than the participants in the low-value group of eHEALS (χ2(3) = 11.115, p = 0.011). Participants in the high-value eHEALS knew that HPV vaccination is needed while young more significantly than the participants in the low-value group of eHEALS (χ2(3) = 8.214, p = 0.042). There is no significant difference in other factors.
| Factors | Answers | eHEALS |
p value
Degree of Freedom χ2-statistic |
|
|---|---|---|---|---|
|
High-value group
(n = 224) |
Low-value group
(n = 217) |
|||
|
knowledge of the HPV vaccine
—the reason for the suspension— |
Knowledgeable |
210 (196.1)
93.8% |
176 (189.9)
81.1% |
p < 0.001
DF*1 = 1 χ2 = 15.005 |
| Unknowledgeable |
14 (27.9)
6.3% |
41 (27.1)
18.9% |
||
|
knowledge of cervical cancer
—effectiveness of the HPV vaccine— |
Strongly agree |
8 (12.2)
3.6% |
16 (11.8)
7.4% |
p < 0.001
DF*1 = 3 χ2 = 18.458 |
| Agree a little |
55 (72.1)
24.6% |
87 (69.9)
40.1% |
||
| Disagree a little |
134 (118.3)
59.8% |
99 (114.7)
45.6% |
||
| Strongly disagree |
27 (21.3)
12.1% |
15 (20.7)
6.9% |
||
|
knowledge of cervical cancer
—HPV vaccination prevents cervical cancer— |
Strongly agree |
65 (50.3)
29.0% |
34 (48.7)
15.7% |
p = 0.001
DF*1 = 2 χ2 = 14.973 |
| Agree a little |
152 (161.0)
67.9% |
165 (156.0)
76.0% |
||
| Disagree a little |
7 (12.7)
3.1% |
18 (12.3)
8.3% |
||
|
knowledge of cervical cancer
—cervical cancer is one of the life-threatening diseases— |
Strongly agree |
96 (82.3)
42.9% |
66 (79.7)
30.4% |
p = 0.003*2
DF*1 = 3 χ2 = 14.190 |
| Agree a little |
114 (120.4)
50.9% |
123 (116.6)
56.7% |
||
| Disagree a little |
12 (20.3)
5.4% |
28 (19.7)
12.9% |
||
| Strongly disagree |
2 (1.0)
0.9% |
0 (1.0)
0% |
||
|
knowledge of cervical cancer
—knowledge of the vaccine type (injection, Oral, etc.) and injection spot— |
Strongly agree |
70 (59.9)
31.3% |
48 (58.1)
22.1% |
p = 0.011
DF*1 = 3 χ2 = 11.115 |
| Agree a little |
79 (72.1)
35.3% |
63 (69.9)
29.0% |
||
| Disagree a little |
49 (60.4)
21.9% |
70 (58.6)
32.3% |
||
| Strongly disagree |
26 (31.5)
11.6% |
36 (30.5)
16.6% |
||
|
knowledge of cervical cancer
—no need for vaccination because of youngness— |
Strongly agree |
0 (2.0)
0% |
4 (2.0)
1.8% |
p = 0.042*2
DF*1 = 3 χ2 = 8.214 |
| Agree a little |
17 (21.8)
7.6% |
26 (21.2)
12.0% |
||
| Disagree a little |
115 (116.8)
51.3% |
115 (113.2)
53.0% |
||
| Strongly disagree |
92 (83.3)
41.1% |
72 (80.7)
33.2% |
||
| HPV vaccination frequency | Never |
131 (131.0)
58.5% |
127 (127.0)
58.5% |
p = 0.707
DF*1 = 3 χ2 = 1.395 |
| Once |
15 (13.7)
6.7% |
12 (13.3)
5.5% |
||
| Twice |
26 (23.4)
11.6% |
20 (22.6)
9.2% |
||
| Completed |
52 (55.9)
23.2% |
58 (54.1)
26.7% |
||
| HPV vaccination request status | Continuing vaccination |
77 (70.2)
34.4% |
58 (64.8)
26.7% |
p = 0.202
DF*1 = 2 χ2 = 3.199 |
| Undecided |
72 (80.0)
32.1% |
82 (74.0)
37.8% |
||
| Never |
23 (21.8)
10.3% |
19 (20.2)
8.8% |
||
|
knowledge of cervical cancer
—the possibility of getting cervical cancer without vaccination— |
Strongly agree |
27 (24.9)
12.1% |
22 (24.1)
10.1% |
p = 0.813
DF*1 = 2 χ2 = 0.413 |
| Agree a little |
145 (146.3)
64.7% |
143 (141.7)
65.9% |
||
| Disagree a little |
52 (52.8)
23.2% |
52 (51.2)
24.0% |
||
|
knowledge of cervical cancer
—cervical cancer is one of the social life-changing diseases— |
Strongly agree |
77 (69.6)
34.4% |
60 (67.4)
27.6% |
p = 0.325*2
DF*1 = 3 χ2 = 3.469 |
| Agree a little |
128 (131.0)
57.1% |
130 (127.0)
59.9% |
||
| Disagree a little |
18 (22.3)
8.0% |
26 (21.7)
12.0% |
||
| Strongly disagree |
1 (1.0)
0.4% |
1 (1.0)
0.5% |
||
|
knowledge of cervical cancer
—The HPV vaccine has a strong side effect— |
Strongly agree |
43 (37.6)
19.2% |
31 (36.4)
14.3% |
p = 0.133*2
DF*1 = 3 χ2 = 5.590 |
| Agree a little |
95 (98.5)
42.4% |
99 (95.5)
45.6% |
||
| Disagree a little |
75 (80.3)
33.5% |
83 (77.7)
38.2% |
||
| Strongly disagree |
11 (7.6)
4.9% |
4 (7.4)
1.8% |
||
|
knowledge of cervical cancer
—The HPV vaccination is painful— |
Strongly agree |
28 (35.0)
12.5% |
41 (34.0)
18.9% |
p = 0.170
DF*1 = 3 χ2 = 5.030 |
| Agree a little |
84 (80.3)
37.5% |
74 (77.7)
34.1% |
||
| Disagree a little |
77 (78.7)
34.4% |
78 (76.3)
35.9% |
||
| Strongly disagree |
35 (30.0)
15.6% |
24 (29.0)
11.1% |
||
|
knowledge of cervical cancer
—no need for vaccination because of no symptoms— |
Strongly agree |
2 (2.0)
0.9% |
2 (2.0)
0.9% |
p = 0.289*2
DF*1 = 3 χ2 = 3.755 |
| Agree a little |
20 (23.4)
8.9% |
26 (22.6)
12.0% |
||
| Disagree a little |
113 (118.9)
50.4% |
121 (115.1)
55.8% |
||
| Strongly disagree |
89 (79.7)
39.7% |
68 (77.3)
31.3% |
||
|
knowledge of cervical cancer
—no need for vaccination because there is no sexual intercourse— |
Strongly agree |
4 (4.6)
1.8% |
5 (4.4)
2.3% |
p = 0.439*2
DF*1 = 3 χ2 = 2.709 |
| Agree a little |
16 (19.8)
7.1% |
23 (19.2)
10.6% |
||
| Disagree a little |
119 (120.9)
53.1% |
119 (117.1)
54.8% |
||
| Strongly disagree |
85 (78.7)
37.9% |
70 (76.3)
32.3% |
||
|
knowledge of cervical cancer
—bothersome— |
Strongly agree |
14 (14.7)
6.3% |
15 (14.3)
6.9% |
p = 0.150
DF*1 = 3 χ2 = 5.325 |
| Agree a little |
86 (97.0)
38.4% |
105 (94.0)
48.4% |
||
| Disagree a little |
82 (75.7)
36.6% |
67 (73.3)
30.9% |
||
| Strongly disagree |
42 (36.6)
18.8% |
30 (35.4)
13.8% |
||
observed frequency (expected frequency)
*1 DF is the abbreviation of “degree of freedom.”
*2 The result of Fisher’s exact test due to the sample sizes.
The effect of the motivation to get the HPV vaccination was analyzed using a multivariable logistic regression analysis using a forward stepwise selection method (Likelihood Ratio). The results of this analysis are displayed in Table 5. We added all the factors from knowledge of cervical cancer shown in Table 4 and the eHEALS level to decide the factors that affect the motivation to get the HPV vaccination. Five factors out of 13 were chosen as the determined factors. Knowing the vaccine type and injection spot of the vaccination was significantly associated with the motivation to get the HPV vaccination (OR = 4.650, 95%CI: 3.291–6.572, p < 0.001). Having the proper knowledge of the side effects of HPV vaccination was also significantly associated with the motivation to get the HPV vaccination (OR = 2.624, 95%CI: 1.807–3.811, p < 0.001). How participants thought to go to get the HPV vaccination, especially non-feeling bothersome, was also significantly associated with the motivation to get the HPV vaccination (OR = 1.831, 95%CI: 1.303–2.573, p < 0.001). Knowing whether or not having the symptoms does not matter to getting vaccination was also significantly associated with the motivation to get the HPV vaccination (OR = 1.815, 95%CI: 1.151–2.862, p = 0.01). Lastly, a low level of eHEALS was also significantly negatively associated with the motivation (OR = 0.522, 95%CI: 0.302–0.901, p = 0.02).
| Factor | B | p value | Odds ratio |
95%
Confidence Intervals |
|---|---|---|---|---|
|
knowledge of cervical cancer —knowledge of the vaccine type (injection, Oral, etc.) and injection spot— |
1.537 | <0.001 | 4.650 | 3.291–6.572 |
|
knowledge of cervical cancer
—proper knowledge of the side effects of HPV vaccination— |
0.965 | <0.001 | 2.624 | 1.807–3.811 |
|
knowledge of cervical cancer
—not bothersome— |
0.605 | <0.001 | 1.831 | 1.303–2.573 |
|
knowledge of cervical cancer
—whether or not having the symptoms does not matter to get vaccination— |
0.596 | 0.01 | 1.815 | 1.151–2.862 |
| Low level of eHEALS | -0.650 | 0.02 | 0.522 | 0.302–0.901 |
n: vaccinated group: 183, unvaccinated group: 258
R2 = 0.57
The present study demonstrates that eHealth literacy affects the motivation to get the HPV vaccination as well as other factors, such as the various knowledge of HPV vaccine/cervical cancer. The average number of eHEALS scores in this study was 22.9/40, the same as the 22.8 points Mitsutake et al. showed in the previous research, even though the age range of the research was 20 years old to 50 years17). The eHEALS scores in this study were distributed unevenly, ranging between 8 points to 39 points. It might be affected by individual experiences such as the experience using the internet in the past.
Knowing the vaccine type and injection spot of the vaccination strongly affected the motivation to get the HPV vaccination in this study. The participants with higher eHealth literacy had the proper knowledge significantly more than those with low levels of eHealth literacy. Miyamoto mentioned that most university students did not know the injection spot of the HPV vaccination19). The HPV vaccination survey provided by MHLW also showed that only 13% of participants aged between 11 and 26 years old knew the way of vaccination20). It must be scary for people to encourage themselves to get the vaccination without knowledge of the vaccination. It will be helpful to encourage people to get the vaccination by showing the vaccination method in the leaflet, which is distributed in the school or somewhere related to the local governments. Contributing knowledge must be considered, as people with low levels of eHealth literacy need the knowledge. It was also shown in this study that the participants who had higher eHealth literacy also had the proper knowledge about the seriousness and susceptibility of cervical cancer. It encouraged them to get the vaccination. The result was different from the previous research that mentioned most university students seemed like they believed they would not contract cervical cancer quickly even if they did not get the vaccination21).
It is probable that the participants in this study were primarily related to the medical field and had a basic knowledge of cervical cancer.
It was also a good motivation for participants who had higher eHealth literacy to get the vaccination by knowing the HPV vaccination affects the prevention of cervical cancer significantly. Those people especially believe that HPV vaccination has a significant effectiveness rather than the side effects. On the other hand, people who do not want to get the HPV vaccination have a feeling of worrying about the side effects. The participants who missed the opportunity of HPV vaccination might have more feelings of worrying about the side effects because the media provided such information on TV back then. It might be challenging to eliminate the feelings of worrying about the side effects altogether, but lessening it would be possible, and providing the information that the HPV vaccination affects the prevention of cervical cancer would be effective.
Mitsutake et al. mentioned that people with low eHealth literacy tend to prefer to obtain health information passively from specific media such as TV and radio17). According to the MHLW survey, 34% of people aged under 26 years old or 55% of their parents are using a TV to obtain health information, including information on HPV vaccination20). Surprisingly, 30% of people aged under 26 years old are not obtaining any health information, including information on HPV vaccination at all. Their parents are more likely to use other sources than their children for getting such information; 26% are obtained from websites, 17% are from their friends, 15% are from doctors, 13% are from newspapers, and so on. The participants in this study mentioned that family thoughts affect their attitudes toward HPV vaccination. We must consider the methods of publicity for parents of under 26 years old children to make them understand the truth of HPV vaccination. A TV and internet source must be considered as practical tools for that. For those people under 26, especially those who do not obtain health information by themselves, compulsory subjects at school, college, or university must be useful for publicity methods. Using a bulletin board, even a digital version, would be helpful. The younger generation is easily affected by social media influencers nowadays, so taking advantage of them would also be an option.
Finally, we only focused on female students in this study. Hamasaki & Tsukahara mentioned most male university students did not have knowledge of HPV vaccination in their study22). They should know they can be infected with HPV and can be the source of infection for their partners. In some countries, it is currently recommended for men to get the HPV vaccination23). We update and examine the information and give the correct data to certain people as health workers.
The present study was subject to several limitations. The departments that participants belong to at the university need to be balanced. We only focused on female students in one university. Future longitudinal studies, including those of male students, may help to confirm the strategy to motivate people to get the HPV vaccination.
In conclusion, we examined what factors affect female university students to encourage HPV vaccination. The eHealth literacy affects the motivation to get the HPV vaccination as well as other factors, such as the various knowledge of HPV vaccine/cervical cancer focusing on female students who missed the opportunity of HPV vaccination due to the government decision. The finding that eHealth literacy affects the motivation to get the HPV vaccination can help people who work in the health, medical, and educational fields to make a strategy to spread the correct information about HPV vaccination to the targeted population. Further studies are needed to examine which sources would be helpful most.
We are indebted to all the research participants. This study was supported by Okayama University annual research aid for a study in 2023 (Yoko Takahata).
All authors contributed directly to this study. AS., MT., and MM. designed the study construction and collected the data. AS, MT, and MM. analyzed the data, and YT. took responsibility for the integrity of the data analysis. All authors drafted the manuscript. This study was conducted as a graduation thesis under the supervision of YT.
The authors declare no conflict of interest.
