Here is an interview with Joshua Coval, of Harvard Business School, about his current research. I would urge caution on interpreting these results, but this is what the data toss back out at us:
Q: One of your findings was that the chairs of powerful congressional committees truly bring home the bacon to their states in the forms of earmark spending. Can you give a sense of how large this effect is?
A: Sure. The average state experiences a 40 to 50 percent increase in earmark spending if its senator becomes chair of one of the top-three committees. In the House, the average is around 20 percent. For broader measures of spending, such as discretionary state-level federal transfers, the increase from being represented by a powerful senator is around 10 percent.
Q: Perhaps the most intriguing finding, at least for me, was the degree and consistency to which federal spending at the state level seemed to be connected with a decrease in corporate spending and employment. Did you suspect this was the case when you started the study?
A: We began by examining how the average firm in a chairman's state was impacted by his ascension. The idea was that this would provide a lower bound on the benefits from being politically connected. It was an enormous surprise, at least to us, to learn that the average firm in the chairman's state did not benefit at all from the increase in spending. Indeed, the firms significantly cut physical and R&D spending, reduce employment, and experience lower sales.
The results show up throughout the past 40 years, in large and small states, in large and small firms, and are most pronounced in geographically concentrated firms and within the industries that are the target of the spending.
For the pointer I thank Alex Prado.
Addendum: Megan McArdle comments on the difficulty of interpretation.