The biggest challenge comes with the fact that you're often dealing with rescue dogs that are so wildly different from one another that you'd need a huge popula

The biggest challenge comes with the fact that you're often dealing with rescue dogs that are so wildly different from one another that you'd need a huge population and extremely consistent methods to show a meaningful result. It's more doable if things are controlled (e.g. take a bunch of German Shepherd puppies given to very experienced trainers at birth), but those circumstances don't necessarily tell you what the "best" method is in a generalizable fashion.