If voters care about the size of the government's majority, then by-election votes should exaggerate national swings. Moreover, if there is uncertainty about the outcome of the general election and if voters” preferences are skewed in such a way as to give more weight to the “downside”...

If voters care about the size of the government's majority, then by-election votes should exaggerate national swings. Moreover, if there is uncertainty about the outcome of the general election and if voters' preferences are skewed in such a way as to give more weight to the 'downside' outcome...