Little attention has been given to the behavior of option portfolio risk across different portfolio sizes, perhaps because many individuals view unhedged long option positions as too risky for rational investor consideration. It appears possible, however, to combine long option positions with less risky assets to produce portfolios with favorable risk-return characteristics [10].

It is often desirable to know whether or not a risky asset's beta coefficient has changed and, if so, at what point in time the change occurred. For example, this knowledge is of obvious importance to beta-using security analysts and portfolio managers. As another example, a given theory may imply that a particular firm's beta should have changed at different points in time. Investigators may want to test such a hypothesis. Furthermore, tests are frequently performed on the effects of events on residuals of the market model, tests requiring the assumption of beta stability. For these, and possibly other reasons, it is useful to be able to detect that a change in beta did, in fact, take place as well as, in some instances, identifying the point in time at which the change took place.

A number of studies have compared the investment risk of various industries and of various individual corporations in developed countries (DCs). The purpose of this paper is to compare investment risk in DCs with less developed countries (LDCs). The variance of returns to investment in common stocks provides a natural measure of investment risk and will be used in this study. Studies in LDCs include work of Levy and Sarnat [12], [13]. Errunza [3], [4], and Lessard [11]. Levy and Sarnat and Errunza found low economy-wide investment risk on an average for LDCs (relative to DCs), with stock indices being used as surrogates for economy-wide risk. These results are not unambiguous, however, because there are probable difficulties due to infrequent trading and averaging in the broad market indices used in the above studies. Hence, we use a sample of the largest corporations that suffer little, if at all, from thin trading and/or averaging.