The conclusion of this article is misleading due to the flaw design of the experiment. First the conclusion (my emphasis):
The purpose of this study was to examine how multiple columns and text justification impact online reading in terms of reading speed, comprehension, and satisfaction of a narrative passage. Results from this study showed that reading speed was significantly faster for two-column full-justified text than for one-column full-justified text. Post-hoc analyses showed that it was the fastest readers that benefited the most from this format.
So, let's get the situation right first. It is for online reading. Next, the conclusion: two-column full-justified text is significantly faster.
My own experience tells me otherwise. In fact, I hate online presentation with multiple columns.
So, where was the flaw of the experiment design. Look at its sample text.
One-Column Full-Justified Condition
Two-Column Full-Justified Condition
The sample text was short, so short that it can be displayed in one screen, hence the experiment result. We know that if the text is longer, we will then need to scroll down to read the rest of column one. After which, we need to scroll up again to the top to read the second column. I don't see any possibility that such a realistic scenario will produce the same result.
Experiment design! Please don't publish any result if the design was flawed. It is wasting everybody's time.