I've come to realize that there's a specific pretty basic topic at the level of college algebra/precalculus which is given competing, contradictory definitions in different textbooks (link). And this topic also shows up at the high school level. I'd like to follow up on this and determine the proportion of students exposed to each type of definition, and ideally a breakdown by geographic location (say, nationality) if possible.
What's the best way to go about determining which college textbooks are most common/ biggest sellers/ used in more classes/ have more students exposed to them (or any related metric)? Or even better: any way to determine what proportion of students are given one of a few different, competing definitions for a topic?