## 3 Materials and Methods
### Recruitment  
The sample size was calculated using a power analysis formula [16]. With a significance level \(\alpha\) = 0.05, power 1-\(\beta\) = 0.80, and medium effect size = 0.3, based on the analysis of variance (ANOVA) test, the minimum sample size for each group was 21. After assuming a 25% dropout rate, each group needed 35 participants for a total of 70 research participants. According to previous research, the median target effect size was 0.3 in the publicly funded Health Technology Assessment trial [17].  
All participants were parents raising 0-35-month-old children who required vaccination in accordance with Korean law. The research participants were provided with information regarding the study. The inclusion and exclusion criteria for study participants were as follows.  
Inclusion criteria:  
1. Parents raising 0-35-month-old children who required vaccination;
2. Parents raising children who were required to be immunized within three months;
3. Parents who could understand the survey and were able to respond;
4. Parents who were raising their first born child;
5. Parents who understood the purpose of this study and who provided a written consent;
6. Kakao Talk app users. Exclusion criteria:  
1. Parents who have career related to the medical field;
2. Parents raising more than one child;
3. Parents who cannot read or communicate in Korean;
4. Parents who refused to participate.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Group** & **Intervention** & \begin{tabular}{c} **Post-Test** \\ **(After 4 Weeks)** \\ \end{tabular} & \
\begin{tabular}{c} **Post-Test** \\ **(After 8 Weeks)** \\ \end{tabular} &
\begin{tabular}{c} **Post-Test** \\ **(After 12 Weeks)** \\ \end{tabular} \\ \hline Experimental & X 1 [FOOTNOTE:1]Footnote 1: X: child vaccination chatbot baseline. 2 EI, E2, E3: Measure child vaccination information, motivation, self-efficacy, and behavioral intention for the experimental group. 3 C1, C2, C3: Measure child vaccination information, motivation, self-efficacy, and behavioral intention for the control group. 3 C1, C2, C3: Measure child vaccination information, motivation, self-efficacy, and behavioral intention for the control group. \\ \hline \hline \end{tabular}
\end{table}
Table 1: The research design of the study.  
The convenience sampling method was used in this study. The participants were randomly recruited online community via \"Mom Cafe\" ([[http://cafe.naver.com/ttokks](http://cafe.naver.com/ttokks)]([http://cafe.naver.com/ttokks](http://cafe.naver.com/ttokks)) accessed on 3 January 2020) by announcing recruitment on the bulletin board for parents who met the inclusion criteria. The participants were recruited online and through social networking services (SNS). The recruitment process lasted from 30 January to 15 February 2020. After the parents provided their consent, they were asked to provide basic information, such as the age of their child, that could be used to develop appropriate groups.  
To retain homogeneity between the control group and the experimental group, parents raising their first child who was younger than 35 months were recruited. To distribute parents evenly in each group, children of a similar age were placed in pairs in the experimental and control groups. The two groups were otherwise randomly assigned. Block randomization was performed using R software (R Foundation for Statistical Computing).  
The initial survey was sent to participants via Kakao Talk using their mobile numbers. A chatbot link was provided via Kakao Talk to the experimental group, while a child vaccination paper brochure was sent to the control group. After 4, 8, and 12 weeks of using the chatbot, the experimental group was asked to evaluate the chatbot using a mobile survey ([[http://forms.gle/byhoq725](http://forms.gle/byhoq725) xYkWBNcn8]([http://forms.gle/byhoq725](http://forms.gle/byhoq725) xYkWBNcn8) accessed on 1 July 2020).