The broad import of the evidence is that the application and qualification by a firm for listing on one of the two major American securities exchanges did, at least during the years encompassed by our investigation, constitute an event with which were associated abnormal positive investment returns on the shares involved. Even though a portion of those returns seem subsequently to have been surrendered, the initial net effect from application through listing date was quite substantial, and the later correction thereto was much more modest. The average combined impact visible in Table 3 during the six-month period beginning with the listing application, for example, was a net positive annualized return approximately 17 percent above that enjoyed concurrently by the general run of comparable-systematic-risk securities in the market. The explicit consideration of such risk distinguishes the present investigation from earlier studies in the area      .
On balance, then, it appears not unreasonable to conclude that listing did indeed “have value” for the companies examined. While one could argue that it was, intrinsically, the corporate developments (and the dissemination of the news thereof) which led to listing that were the real sources of value, the observed concentration of excess returns in the close proximity of the various application and listing dates would suggest that those actions provided useful market signals which did, in themselves, have a detectable favorable payoff—perhaps if only by way of accelerating the investment community's appreciation of the improvement in the applying firm's underlying operating circumstances. We interpret the evidence as supportive of that hypothesis.
The implications of the same evidence for questions of market efficiency, however, are somewhat more ambiguous. There would seem, as noted, to be in the data indications of certain possible information-response time lags that are not totally consistent with efficiency; and there is an apparent systematic initial price overreaction to application-cum-listing which is later remedied. Transactions costs, on the other hand, have not been considered here, and these clearly would impede the adjustment process by raising the threshold for investor action. Despite some cause for suspicion, therefore, a definitive judgment about efficiency must await further investigation.