No specific study per se was undertaken.
What I would note is that companies have the ability to either use the proxy amount or claim their actual overhead expenditures. While the proxy amount is being gradually reduced, companies retain the option of tracking actual expenses and claiming whichever amount is more advantageous to them.
It's also unlikely that one proxy amount would cover or reflect all industries. To establish one that is unique may not have been a profitable undertaking. A proxy, again, is a simplified method. Canada is actually the only country that offers SR and ED claimants the ability to use a proxy amount.