18
75
th
percentile value. We also show the change in predicted probability moving from the
25
th
to the 75
th
percentiles.
[Table 5 about here]
Table 5 provides further support for the proposition that electoral circumstances
are more important than ideological distance for explaining the allocation of leadership
PAC contributions. Out of eight sets of results (two parties times two time periods times
two candidate types), the change in predicted probability due to a shift in electoral margin
exceeds the change due to a shift in ideology for both extreme and moderate candidates
in every instance. Also, leadership PAC sponsors are more likely to support their fellow
incumbents than open seat candidates and challengers, although the difference is much
greater for Democrats than Republicans. We have no theoretical explanation for this
party difference, and it should be remembered that these results represent the central
tendency of many individual PACs. Nonetheless, the pattern is robust.
Table 5 also demonstrates the lack of evidence for two theoretically plausible
distinctions. First, we find no systematic evidence of strategic behavior with regard to
ideological differences. The effects of ideological distance are negative for all but
extremist Republican incumbents in 1983-1988, but it is not generally the case that the
effects are greater (more negative) for extremists than moderates. The difference in the
coefficients for extremist and moderate candidates is statistically significant at the 95
percent confidence level only for Republican and Democratic incumbents in 1983-1988
and Republicans in 1995-2000. However, in two of these cases, the effect of ideology is
more negative for moderates than extremists. Second, the predicted effects of a change in
electoral margin are slightly larger for Democrats in the 1990s than the 1980s, but the
Convention