I think Trende is right that turnout in primaries is more a function of the level of competition within the party that year rather than an omen for the general election. But unfortunately, he only uses total numbers of voters in those primaries to analyze the question. I used his table and combined it with estimates of voter party affiliation and total numbers of registered voters to generate an indicator of voter turnout in out-party primaries. This allows us to address the question of whether turnout in the primaries of the party not currently in control of the White House affects the vote share in November. Here's a scatterplot (the points are labeled by the candidate of the incumbent party):
The results above suggest a negative correlation, implying that lower participation in out-party primaries is associated with a higher vote share for the incumbent party's candidate. For this year, that would mean that if Republican primaries are really suffering from low turnout, that would favor Obama.
Now, some important caveats:
- The relationship shown above is not statistically significant and is further washed away when one controls for economic growth.
- The relationship shown above is based on a small number of cases (from 1972 on).
- The measurement of turnout in primaries is imperfect. I'm using an estimate of all those who identified with the party in my denominator, but different state party rules strongly affect who gets to turn out. (e.g.: Democratic leaners, whom I include, might have a harder time participating in a closed primary than in an open one.) I'm open to better data if anyone has any.