We conducted an intervention study using SONY's aibo, dividing caregivers and children who came to the hospital for Japanese encephalitis vaccination into an intervention group and a control group, in accordance with our objectives. The following is a description of the study subjects, survey period, intervention method, contents of the survey and analysis method in the study.
1. Study subjects
The subjects were children between the ages of 3 and 12years old eligible for the Japanese encephalitis vaccine, and their caregivers.
2. Survey period
The survey period was February 2020 to December 2020.
3. Intervention method
One children's clinic in Mitaka City, Tokyo, which provides general pediatric care, was asked to cooperate in the study. The survey procedure is shown in Figure 2. A staff member (psychologist or physician) from the National Center for Child Health and Development (NCCHD) visited the clinic once a week as an observer and asked the caregivers and children for their cooperation while in a waiting room (small enough to accommodate 3 to 4 pairs of caregivers and children) exclusively for those scheduled for vaccination. Those who visited the clinic in odd-numbered months were assigned to the intervention group, and those who visited the clinic in even-numbered months were assigned to the control group. After obtaining caregiver’s consent, children and their caregivers were asked to spend time with aibo or a stuffed dog during the waiting time before and after child's vaccination (about 5 minutes each) in a waiting room, and children’s behavior was observed by professional observers. The children evaluated their pain experience after 5 minutes each whereas their caregivers proxy answered when child was not able to answered. If the aibo got stuck or the stuffed dog fell down, the observer adjusted the situation accordingly. The total survey time for each caregiver-child pair was about 15-20 minutes.
The dimensions of aibo (Figure 1) used in the intervention group were 180 × 293 × 305 mm and it weighed 2.2 kg. It was able to move freely around the waiting room. Its eyes were equipped with OLED displays, and it showed rich facial expressions as well as various voices and behaviors. It also responded to stimuli from touch sensors on its head, neck, and back with facial expressions and voices. The stuffed dog used in the control group was a gray-haired stuffed animal measuring 130 × 320 × 330 mm in length. It could change the angle of its limbs and neck but it did not move spontaneously and was not equipped with any special functions, such as voice or behavior.
4. Contents of the survey
The following indices were used to evaluate pain, distress, and restlessness.
(1) Primary index: Evaluation of pain and anxiety using Faces pain rating scale (FS)
The FS is a scale that describes a person's facial expressions at several levels, and evaluates feelings and states by facial expressions in addition words or numbers. In the present study, the Wong Baker faces pain scale  was used (Figure 3). It has six levels of facial expressions ranging from a smiling face to a crying face. Each expression was assigned a number on scale of 0, 2, 4, 6, 8, and 10, with a lower number indicating less pain and a higher number indicating more pain.
(2) Secondary indicator: Behavioral observations using the observer pain scale
The observer pain scale was translated from the scale reported by Gracely et al. . Children were observed interacting with aibo or a stuffed dog immediately after vaccination called “immediately following (IF)” and 5 minutes after vaccination called “post”, and the observer rated them. The observer evaluates the child's behavior and state on a scale of 1 to 5, with 3 being normal and calm, a lower score indicating that the child is active and upset, and a higher score indicating that the child is in pain and distress. In order to ensure that there were no differences in observation and scoring among the raters, meetings were held within the raters to standardize the scores.
5. Analysis method
The mean values of the FS and the observer pain scale scores at each time point before and after vaccination were calculated for each group, and the differences in the mean values at each time point were compared between groups using an unpaired t-test (significance level 5%, two-tailed test)