The relevance or otherwise of the central bank's balance sheet

That is not to say that the big expansion of central bank balance sheets in recent years has been ineffective. Our finding is rather that the portfolio balance channel evaluated in an environment of normally functioning (though nonetheless incomplete) asset markets is weak. That is not inconsistent with the evidence that large-scale asset purchases by central banks since 2008 have had significant effects, because those purchases were made when financial markets were, to varying extents, dysfunctional. Nonetheless our results are relevant to those purchases because they may be unwound in an environment where financial markets are no longer dysfunctional.