BY-ELECTIONS, CHANGING FORTUNES, UNCERTAINTY AND THE MIDTERM BLUES

If voters care about the size of the government's majority, then by-el ection 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 ''d ownside'' outcome (least favourite party wins) than the ''upside'' (fa voured party wins with a larger than preferred majority), then there w ill be a systematic tendency for governments to lose by-elections, reg ardless of any changes in national support. These predictions go beyon d those generated by conventional explanations. The theory is successf ully tested against data from 383 post-War elections.