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Book of Value - The Fine Art of Investing Wisely 2016(AnuragSharma)
https://bbs.pinggu.org/forum.php?mod=viewthread&tid=6303889&from^^uid=109341(Page 247-252)
阅读到的有价值的内容段落摘录
Diversification and Modern Portfolio theory
Around 1950, before Markowitz, intuition about the benefits ofdiversification was well established. That this was common knowledge is evident,for instance, in the well-known 1924 book Common Stocks as LongTerm Investments by Edgar Lawrence Smith. But noobjective measures of risk existed at the time, especially for the joint riskof a bundle of investments. So, Markowitz took up this problem as a topic forhis doctoral dissertation in economics and, using concepts from the statisticstexts of the time, formalized the concept of portfolio risk. In particular, hedefined the risk of a stock as the standard deviation of its returns and thenformulated portfolio, or joint, risk using conditional probabilities, orcovariances of returns of all stocks in the portfolio. Of special note inMarkowitz’s equation was the correlation between the stocks in the portfolio.3If the returns correlate perfectly, then portfolio riskcomputes relatively simply and is for the most part
uninteresting, as investors wouldinstinctively know to try to avoid having two such stocks in their portfolio..That is simple enough. But what excited Markowitz was that most stocks did notmove in perfect unison. Subject to the same systemic factors, such as theeconomy and political invironment, correlation between stocks was usuallypartial but almost never zero. It was such imperfect correlations that made thepractical implications noteworthy.
In order to reduce portfolio risk sodefined, investors now had to solve the problem of finding stocks that hadminimal or even negative correlations. But Markowitz went a step further: hedefined efficient portfolios as those groupings in which the proportion of eachstock is such that the portfolio risk is minimal for a given expected return ofthe portfolio. As the number of stocks in the portfolio increased, the numberof terms in the Markowitz equation multiplied fast; calculating portfolio varianceand risk became computationally intense. But, with increasing computationalpower, such math became less and less of a problem. In essence, Markowitz’sgenius was in showing how to lower investment risk, mathematically andspecifically, by grouping unrelated stocks into a portfolio. An implication ofthis formulation was that investors ought to be thinking of risk not in termsof single stocks but in terms of portfolios of stocks. Particularly fascinatingwas the corollary that the risk (or valuation) of a single stock by itselfshould mean very little in large, well-diversified portfolios. The number ofcovariance terms increases as the size of the portfolio increases, and theyovershadow the effect of the weighted variance of any one stock. When you add asingle stock to an existing portfolio of 30 stocks, for example, the new stock adds its own weightedvariance term but also 30 covarianceterms—the covariance of the new stock with each of the already existing stocks.These 30 additionalcovariance terms influence the change in portfolio risk much more than the riskof one new stock by itself.
Twoimplications are usually derived from the math of computing portfolio variance:(1) the risk of a single stock does notmatter that much; and (2) eachbuy or sell decision must be made in light of whatever stocks you already havein the portfolio. As we will see later, the second implication is certainlyvery helpful, but the first implication that the risk of any one stock does notmatter is patently misleading. At the time, though, this was breakthroughthinking, and Markowitz earned a Nobel Prize for conceiving portfolio risk andespecially for delivering the math to make it possible. This way of thinkingabout investing revolutionized finance and is now deeply entrenched in
investmenteducation. One of the early extensions to Markowitz’s work was by WilliamSharpe, with his idea that the risk of a single stock ought to be evaluated inrelation to the overall market risk. Think of a fully diversified investor whoowns a basket filled with all the stocks in the market. To that market basketyou want to add another stock; the issue is the degree to which that additionalstock will increase or decrease the risk of the market portfolio. This concept,beta (β), is simply a mathematical formulation that normalizescovariance between the stock and the market basket (index)—usually approximatedby the S&P 500 Index.This formulation
madeit possible for each stock to have a number, β, that captured its covariance with the overall market. Othermodifications followed, but the core ideas that took hold were that we canapproximate the risk of a stock with a simple statistic (standard deviation)and that we can compute portfolio risk using returns data for each stock in theportfolio.
阅读到的有价值信息的自我思考点评感想
For value investing differs from modernportfolio theory in its focus on subjectively but deeply understanding the wealth-creatingmechanisms of businesses, and the difficulties and uncertainties that managersface as they construct and operate such mechanisms. It is this focus on thebusiness that was the intent of Graham and Dodd and, I’d argue, has been thebasis for the long-term success of many professional investors, includingWarren Buffett. All
these investors clearly recognize that, asEdgar Lawrence Smith had intuitively practiced and Graham had repeatedlyargued, investing is a group operation; spreading the bets intelligently acrosscompanies in a portfolio is sound practice. Markowitz tried to formalize thisidea and got it mostly right in theoretical terms, but the field of finance hasnot quite followed through with a credible and robust way to proxy for thetheoretical chance that investors might lose their invested principal. I submitthat the arms-length mathematical approach simply cannot adequately capture thecomplex of factors that comprise true risk. We need to understand thewealth-creating machinery by getting up close with the businesses in which weinvest.
Diversification will lower the risk of wrong investment,but it will also lower the profit even the investment is correct. Value investingis more concentrate on small number of portfolio. Value investing will concentrateat fewer portfolios. Most people will pick around 5-10 stocks of differentindustries to invest.