Comcast shareholders may hope they're the exception to the trend identified in this 1997 Journal of Finance study, one of the most well-known M&A academic papers of recent years, widely cited in both the academic and popular press. After examining 947 corporate acquisitions that took place between 1970 and 1989, the University of Iowa scholars concluded:

Mergers are usually friendly to the target managers, but, on average, they are not in the best interests of long-term shareholders. Tender offers are usually hostile to the target managers, but seem to benefit long-term shareholders.

Second, we believe that managers use stock payment when the acquirer stock is overpriced. Thus, target shareholders who receive acquirer stock in exchange for their holding should sell out for cash when they receive that stock. And target shareholders who receive cash would be well advised to go to the market and buy the acquirer stock.

In other words, companies often have overvalued shares if they're using that stock to buy other companies.

People rooting for Comcast may take more heart from this 1999 Business Economics paper by a pair of UCLA researchers.

The data compiled earlier by Loughran and Vijh compares acquiring firms to "matching" companies that have similar financial market-to-book and price-to-earnings values. On that basis, the 1997 study concluded that acquirers are negative performers. However, Weston and Jawien point out that on an absolute basis, shareholders of acquiring firms achieved a compound annual return of 62 percent over five years. While that figure is below the 87 percent return of "matching" companies, it still equates to a 10.1 percent compound annual return, which many people would consider at least a decent return.

The UCLA duo suggests that acquirers may have been in industries with more turmoil at the time of the acquisitions than the industries of the "matching" companies. Although Weston and Jawien don't go farther than that statement, others may conclude that without acquisitions, the acquirers might have done even worse because of their chaotic industry situations. And there's no denying that the cable and media industries are a fluid market right now.

For this paper published last year, the professors from Southern Methodist University, the University of Pittsburgh and Ohio State University took an extremely broad sample of data: 12,023 acquisitions from 1980 to 2001. On the surface, their research paints a depressing picture for all acquiring companies:

"Shareholders of these (acquiring) firms lost a total of $218 billion when acquisitions were announced. Though shareholders lose throughout our sample period, losses associated with acquisition announcements after 1997 are dramatic."

But it's not quite that cut and dried. Shareholders of small firms actually gained $8 billion after their acquisitions:

Small firm shareholders earn systematically more when acquisitions are announced. This size effect is typically more important than how an acquisition is financed and than the organizational form of the assets acquired.

Unfortunately for those rooting for Comcast, large firms generally don't do so well with their purchases, although the professors can't specifically explain why:

Our evidence is consistent with the hypothesis that agency problems in large firms lead them to make poor acquisitions. It is also possible, however, that large firms that make acquisitions are the firms that signal that they have exhausted internal growth opportunities, so that firm value drops as a result of that signal rather than because of the acquisition….

Our result that large firms make poor acquisitions when the acquisitions are evaluated using announcement abnormal returns shows that acquisition abnormal returns are poorly suited to analyses of the social benefits of acquisitions.