To add to my previous comment, a half-page sample of text is no more representative of an entire document than a 100-meter sprint is representative of a marathon. The difference matters. LaTeX's advantage over Word is most pronounced at the large scale.

To give a typical example, running a global search-and-replace within equations is impossible in MS Word, and very easy in LaTeX. Needless to say, this study fails to measure efficiencies of these kinds in any way.

It is actually rather alarming that the study authors are seemingly completely unaware of the difference between page-level efficiency and document-level efficiency.