چه چیزی باعث ارزش بازار شرکت ها در صنایع پدافند شده است؟

This article assesses the relative importance of different types of news in driving significant stock price changes in the defense industry. We implement a systematic event study with the 58 largest publicly listed companies in the defense industry, over the time period 1995–2005. We first identify, for each firm, the statistically significant abnormal returns over the time period. Then, we look for information releases likely to cause such stock price movements. Most of the key drivers in the defense industry are the same as in other industries (key role of formal earnings announcements and analysts’ recommendations) but we also identify some specific features, in particular the influence of geopolitical events and the relevance and frequency of bids and contracts on stock prices. Finally, we examine the impact of the September 11 terrorist attacks on defense firms.

This article assesses the relative importance of different types of news in driving significant changes in firms’ market value in the defense industry. Many studies place great emphasis on the changing nature of the defense industry. Since the end of the Cold War, almost all defense firms have been affected by liberalization, far-reaching structural changes and concentration processes, and one can argue that defense firms have lost their singular status. However, some specific features of the defense industry remain: the oligopolistic structure of the market, the close relationships between defense firms and governments, the key role of public budgets devoted to military expenditure, the high level of R&D, the influence on firms of geopolitical events, etc.

This study seeks to determine whether defense firms’ largest stock price changes are driven by macroeconomic, microeconomic, or non-economic events, or just noise. The distinctive features of the defense industry motivate such a study. The traditional method of event studies is limited by the necessary a priori definition of the categories of events. Therefore, we adopt an alternative methodology to explore the relationship between information events and stock price changes. We first identify, for a given firm, the statistically significant abnormal returns over the time period. Secondly, we look for information releases likely to cause such abnormal returns. Moreover, we consider time-varying beta estimates and a GARCH process to model the volatility. Our sample consists of the 58 largest listed firms in the defense industry. For each firm, we focus mainly on the 10 largest significant abnormal returns (5 up and 5 down) over the 1995–2005 time period.