*6.4. Limitations and Future Directions*

There are some shortcomings in this study. First, the survey in this study is limited to Shanghai, while the sample size is insufficient; thus, there may be some problems with representativeness, and future studies are encouraged to adopt more representative research methods, such as big data analysis of the epidemic. Second, the "perceived inconvenience" in this study is a broad concept, which can be further subdivided into travel inconvenience, privacy concerns, and so on, in subsequent studies. Finally, the number of elderly respondents in this study was small, while the elderly are considered to be a very important group in the prevention of COVID-19; it is expected that future studies on the use of DCTAs among the elderly can be conducted.

**Author Contributions:** Conceptualization, J.C. and D.L.; methodology, J.C.; software, M.S.; validation, G.Z. and M.S.; formal analysis, G.Z. and M.S.; investigation, M.S.; data curation, D.L.; writing—original draft preparation, J.C.; writing—review and editing, J.C. and D.L.; supervision, M.S.; project administration, D.L. and M.S. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data presented in this study are available upon request from the corresponding author. The data are not publicly available for ethical reasons.

**Conflicts of Interest:** The authors declare no conflict of interest.
