Funding for this research was provided by:
National Natural Science Foundation of China (81300814)
Received: 19 April 2019
Accepted: 10 September 2019
First Online: 15 November 2019
Ethics approval and consent to participate
: All data obtained from iOS App stores or 360 Android Stores was open-access. Ethics approval and consent to participate were not applicable in this study.
: Not applicable.
: All authors report no conflicts of interest.