The tax deduction for mortgage interest does not increase homeownership, according to a new study based on an experiment in Denmark.

That finding, which is highly relevant for the tax reform that Republicans are currently mulling that could curb the deduction over the housing lobby’s objections, comes from a working paper released by the National Bureau of Economic Research Monday. The paper, which has not gone through peer review, is co-authored by MIT economist Jonathan Gruber, often referred to as the architect of Obamacare.