Yes, I recall defining measures as being one of the problems with it discussed before, and it may be why I can't find any literature on it. The closest I can come is that the measure of effort is relative to prior measures of work on the same task. For example, in economics you seek to...
I think the 2nd law of thermodynamics, which places limits on the efficiency of thermal engines, can also be interpreted as saying increasing efforts to improve efficiency result in geometrically decreasing results. I can't find that stated, though. I suppose it's just the first derivative...