## 4 Discussion
The single-case design, also known as single-subject design, refers to a research design that can only use one subject in the research process. Although there is only one subject, it can also clearly determine whether there is a causal relationship between variables. However, all the studies did not use the randomized experiment design. This is because individual differences are normally large along the autism disorder spectrum and have different performances in each; therefore, treatment usually focuses only on a single individual's development rather than a group. Multiple baselines across subject design are regarded as a standard and evidence-based method in many computer-based treatments used in special education. It is a fundamental experimental method for research in the field, and, in actual practice, it does not require control groups or many participants. Based on this, maybe it is better to design a multiple baseline across subject design than a posttest or pretest-posttest single-case design. In the study conducted by [PERSON] et al. [68], the author used different evaluators before and after the test, and the sample size is too small. The number of participants and the factors that may affect reliability during the research process should be considered. In addition, studies without research design are also a major issue for the research effectiveness in this area. Measurement methods are also the main concerns in research projects. In the methods used in these studies, both survey research and qualitative research require human participation, and it will increase the error rate and reduce the effectiveness and reliability of the measurement if observers are not adequately trained. Comprehensive training of observers before the intervention, calculating the data multiple times, or using a computer-assisted data collection method can reduce the inadvertent introduction of personnel errors. Furthermore, eye tracking is a technique used to measure a person's eye movements when interacting with a stimulus [87]. [PERSON] et al. [88] examined the utility of eye-tracking as an outcome measure and stated that it has the potential to function as a valid treatment outcome measure for use with individuals with ASD of varying ages and levels of impairment. [PERSON] et al. [89] assessed the ability to search for web information in individuals with high-functioning autism. [PERSON] et al. [90] assessed visual preferences for mobile device interfaces in individuals with autism. [PERSON] et al. [91] applied eye-movement tracking to the diagnosis of high-functioning autism in adults using web stimuli. However, there is still a gap that directly uses eye-tracking technology to measure the AR intervention outcomes. Based on the current findings, future studies could investigate eye-tracking technology as a measure in pre-and post-intervention to track responses to intervention in individuals with ASD. The outcomes reveal that the application of mobile AR in the field of autism intervention is successful to a certain extent. All the studies report a positive result related to target skills. From the perspective of target skills, the achievements are all related to the education of defect repair and improvement of basic life skills of the autistic population. It is to be noted that the research on defect repairment and is much larger than the research on education. This is consistent with the core goal of autistic population interventions, which is to reduce core symptoms or related defects, achieve self-care in life, improve quality of life and reduce family stress, rather than pursuing academic success [92]. From the perspective of outcome measurement methods, studies using survey and qualitative research measurement methods both report better various performances and the improvement of participants' capabilities, and studies using scaling give the scores improvement of participants. The studies without user research only mention the usability of related apps.