外文翻译---股票：期望收益和未期望收益(编辑修改稿)

外文翻译---股票：期望收益和未期望收益(编辑修改稿)内容摘要：

ecap stocks. The biggest individual gainers for the year were Intel (up 107 percent), Caterpillar (up 86 percent), and Alcoa (up 71 percent). But not all 30 stocks were up: the losers included Eastman Kodak (down 24 percent.) ATamp。 T (down 19 percent), and Merck (down 11 percent). In contrast to 2020, consider 2020 when the DJIA was down about 17 percent, a fairly bad year. The big losers in this year were Home Depot (down 52 percent), and Intel (down 50 percent). Working to offset these losses was Eastman Kodak (up 20 percent). Again, the lesson is clear: diversification reduces exposure to extreme outes, both good and bad. Diversification and unsystematic risk From our discussion of portfolio risk, we know that some of the risk associated with individual assets can be diversified away and some cannot. We are left with an obvious question: why is this so? It turns out that the answer hingers on the distinction we made earlier between systematic and unsystematic risk. By definition, an unsystematic risk is one that is particular to a single asset or, at most, a small group. For example, if the asset under consideration is stock in a single pany, the discovery of positive NPV projects such as successful new products and innovative cost saving will tend to increase the value of the stock. Unanticipated lawsuits, industrial accidents, strikes, and similar events will tend to decrease future cash flows and thereby reduce share value. Here is the important observation: if we only held a single stock, then the value of our investment would fluctuate because of panyspecific events. If we hold a large portfolio, on the other hand, some of the stocks in the portfolio will go up in value because of positive panyspecific events and some will go down in value because of negative events. The effect on the overall value of the portfolio will be relatively small, however, because these effects will tend to cancel each other out. Now we see why some of the variability associated with individual assets is eliminated by diversification. When we bine assets into portfolios, the unique, or unsystematic, eventsboth positive and negativetend to “wash out” once we have more than just a few assets. This is an important point that bears repeating: Unsystematic risk is essentially eliminated by diversification, so a portfolio with many assets has almost no unsystematic risk. In fact, the terms diversifiable risk and unsystematic risk are often used interchangeably. Diversification and systematic risk We’ve seen that unsystematic risk can be eliminated by diversifying. What about systematic risk? Can it also be eliminated by diversification? The answer is no because, by definition, a systematic risk affects almost all assets to some degree. As a result, no matter how many assets we put into a portfolio, the systematic risk does not go away. Thus, for obvious reasons, the terms systematic risk and nondiversifiable risk are used interchangeably. Because we have introduced so many different terms, it is useful to summarize our discussion before moving on. What we have seen is that the total risk of an investment, as measured by the standard deviation of its return, can be written as: Total risk = systematic risk + unsystematic risk Systematic risk is also called nondiversifiable risk or market risk. Unsystematic risk is also called diversifiable risk, unique risk, or assetspecific risk. For a welldiversified portfolio, the unsystematic risk is negligible. For such a portfolio, essentially all of the risk is systematic. Definition of the market equilibrium portfolio Much of our analysis thus far concerns one investor. His estimates of the expected returns and variances for individual securities and the covariances between pairs of securities are his and his alone. Other investors would obviously have different estimates of the above variables. However, the estimates might not vary much because all investors would be forming expectations from the same data on past price movements and other publicly available information. Financial economists often imagine a world where all investors possess the same estimates on expected returns, variances and covariances. Though this can never be literally true, it can be thought of as a useful simplifying assumption in a world where investors have access to similar sources of information. This assumption is called homogeneous expectations. If all investors had homogeneous expectations, would be the same for all individuals. That is, all investors would sketch out the same efficient set of risky assets because they would be working with the same inputs. Th。