Assuming the categories are meant to apply to any data sets, anything amenable to machine learning at all is at least medium data. "Small" data would be somethi

Assuming the categories are meant to apply to any data sets, anything amenable to machine learning at all is at least medium data. "Small" data would be something like a human trial with n=6 because the length and compliance of the protocol is so onerous. There are entirely different statistical techniques for finding significance in the face of extremely low power.