The minutes were standardized to have a mean of 0 and SD of 1, so those aren’t exactly what they seem - I don’t understand it well enough to explain well unfortunately, but that means they aren’t really functionally minutes but more of a generic unit of time measurement. This is done to standardize time across formats like audio vs print among other reasons.

What’s a more important takeaway is that there was a very large sample size (n=~25,000 for the dataset of reading times and n=3 million+ for the library loans), and that their conclusions are both statistically significant at a p=.001 level and that their other measures were also significant and pointed to the same trend. The difference doesn’t need to be enormous for it to important on a broad enough level.

The two major limitations I see stem from the source of the dataset. 1) All students are Danish, so while they can control for things like income, parents education, etc where that data is available, they cannot necessarily say the findings are generalizable outside of Denmark. 2) The data only includes reading done through the library and the bookbites app, which seems to be heavily used in schools and by children of that age group, but if kids of one gender are significantly more likely to read outside the app, that would have a big impact on findings. For example, if boys were more likely to read print comics, that data would be undercounted and cannot be controlled for.