Fig. 3

The flowchart indicates the main stages of literature collections and selections and the corresponding results of relevant literature. The stages are identification, in which all literature containing a keyword is collected from databases such as Google Scholar; screening, in which the duplicated literature is removed; eligibility, in which the collected literature is further filtered based on the review aim; and inclusion, which is the last stage and aims to select the most suitable literature to be involved in the review. The symbol (n) indicates the number of literature at each stage, illustrating the filtration process to get the most suitable literature for the review.