Refinement of the search results
From 2,180 articles in Table 1, some articles appear in both three-level and four-level search results. Also among these are short non-refereed articles and those published in commercial magazines which are not regarded as scientific contributions.
Two of the more senior authors went through 2,180 references for further refinement of the search results to eliminate duplications, non-refereed articles, commercial magazine papers, papers with unknown author names, and some other
papers that were recognized as outliers. The refinement resulted in 338 journal articles published between 1975 and 2014
(note: that we imposed no time restriction on the Scopus search attempts). To create the corresponding refinements in the RIS file, the RIS data was imported to Endnote bibliography software, the elimination of papers was completed in Endnote and the format was reconverted to RIS. The resulting RIS file is used for further data analysis