The Fallacy of Comparing Yields

I see articles from time to time suggesting that organic yields can be equivalent to conventional yields.  Inevitably, they compare an organic field using very high labor and energy applied (in other words, relatively unconstrained in their use of certain inputs) to a conventional field that has to be profitable on world commodity price levels (in other words, constrained in their use of inputs).  The only way to properly compare the two is to hold the state variables constant. 

What I mean by that is that in order for yield comparisons to be done with some reasonable sense of accuracy it has to be done for a given amount of energy, for a given amount of labor and equivalent fields with equivalent moisture and drainage, etc.  This is simply not happening.  Comparisons are made between high input organic farms like the Rodale test farm against USDA average numbers for the county in question or nationally.  It would also be interesting to compare yields for a given amount of expense whether that expense is used for energy, labor, fertilizer or transportation while holding field, soils, drainage, moisture, etc. constant.