阿尔法究竟为何物?
Memo to:
Memo to:
Oaktree Clients
Oaktree Clients
From:
From:
Howard Marks
Howard Marks
Re:
Re:
这一切究竟是为了什么,阿尔法?
What's It All About, Alpha?
先向伯特·巴卡拉克和迪翁·沃里克致歉,他们 1966 年为电影《阿尔菲》演唱的版本艺术性高得多,但我还是忍不住借用他们的歌名来写一份投资理论备忘录。
这一切到底是为了什么?确实如此。每个人都在谈论阿尔法……贝塔、风险与回报、有效与无效。但我相信,没有几个人对它们的理解一致,或者说是正确的。因此,四月份在写《安全第一》时对阿尔法的思考,让我下定决心,把我在所有这些话题上的观点系统地整理出来。
在这点上,1967 至 1969 年我在芝加哥大学商学院的学习经历是关键。我之前就读的是不谈理论的沃顿商学院,在那里我学到了格雷厄姆和多德式的投资实践,但对下面要讨论的内容一无所知。在芝加哥,我接触到一种将彻底改变投资领域的新理论。这次接触让我大开眼界,也使我避免成为我所说的“我知道”学派(那些人认为只要稍加努力就能预知任何股票或市场的未来走向)中不加质疑的一员。离开芝加哥后的 32 年,时间足够让我遗忘当年学到的许多理论……但更重要的是,也给了我必要的现实世界经验来调和这些理论,最终形成我自己对理论与实践的综合。
市场有效性——一个人如何看待投资世界,很大程度上取决于他对市场有效性这个问题的立场。与其重新发明轮子,不如直接引用我 2000 年 5 月备忘录《非理性繁荣》中的部分内容。(幸好,抄自己不算抄袭。)
With apologies to Burt Bacharach and Dionne Warwick, whose 1966 rendition for the movie "Alfie" was much more artistic, I couldn't resist adapting their title for a memo on investment theory. What's it all about, indeed? Everyone talks about alpha . . . and beta, risk and return, and efficiency and inefficiency. But I believe few people use them to mean the same thing, or correctly. Thus the thinking I did about alpha while writing "Safety First" in April has convinced me to set out my views on all of these subjects. In this connection, my 1967-69 attendance at the University of Chicago Graduate School of Business was pivotal. I had previously been at a non-theoretical Wharton, where I learned investment practice à la Graham and Dodd but not one word on what I'm about to discuss. At Chicago I found a new theory of investments that would revolutionize the field. My exposure to it was eye-opening and kept me from becoming an unquestioning member of what I call the "I know" school of investing (where people think a little effort is all it takes to know the future direction of any stock or market). The 32 years since Chicago have given me enough time to forget a lot of the theory I learned . . . but also, most importantly, the real-world experience needed to leaven it, leading to my own synthesis of theory and practice. Market efficiency – A great deal of how one views the investment world depends on one's position on the subject of market efficiency. Rather than reinvent my own wheel, I'll lift parts of my memo "Irrational Exuberance" from May 2000. (Thankfully, when you copy from yourself it's not plagiarism.)
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首先,我会谈谈我对有效市场理论支持者观点的看法。接着,我会描述我自己对市场有效性的理解。我得再次承认,学术界并不认同我的观点,理论也说我错了。但我的方法对我管用,下面我会重新阐述一遍。在芝加哥求学时,我最早研究的东西之一就是有效市场假说,其内容如下:
First, I'll provide my take on the efficient marketeers' view. Then, I'll describe my own version of market efficiency. I'll admit again that academicians don't share my view and theory says I'm wrong. But my approach works for me, and I'll restate it below. While at Chicago, one of the first things I studied was the Efficient Market Hypothesis, which states:
市场上参与者众多,对相关信息的获取机会大致均等。他们聪明、动力十足且勤奋努力。他们的分析模型广为人知并被普遍采用。
There are many participants in the markets, and they share roughly equal access to all relevant information. They are intelligent, highly motivated and hard working. Their analytical models are widely known and employed.
由于这些参与者的集体努力,信息得以充分且即时地反映在每项资产的市场价格中。
Because of the collective efforts of these participants, information is reflected fully and immediately in the market price of each asset.
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因此,市场价格提供了资产内在价值的准确估计,任何参与者都无法持续识别并利用市场出错时的机会获利。
Thus, market prices provide accurate estimates of assets' intrinsic value, and no participant can consistently identify and profit from instances when they are wrong.
因此,资产的售价所对应的预期风险调整后回报,相对于其他资产而言是“公平”的。风险更高的资产必须提供更高的回报才能吸引买家。市场会设定价格,使之看起来确实如此,但它不会提供“免费的午餐”。也就是说,不存在与额外风险无关(或非作为其补偿)的额外回报。
Assets therefore sell at prices from which they can be expected to deliver riskadjusted returns that are "fair" relative to other assets. Riskier assets must offer higher returns in order to attract buyers. The market will set prices so that appears to be the case, but it won't provide a "free lunch." That is, there will be no incremental return that is not related to (and compensatory for) incremental risk.
我坚信某些市场相当高效,包括世界主要股票和债券的市场。以国际固定收益市场为例,投资者会判断英国、法国或德国政府债券在某一时点哪个最便宜,并据此调整投资组合权重。在我看来,这些债券的主要差异在于发行国的经济增长率和通胀率。但正是为了弥补这些差异,才存在不同的利率和浮动汇率。这些难道不是全球最受关注的现象之一吗,每个问题的正反两面都有数百家老练的金融机构在角逐?现实中,有哪个参与者能指望在这样的市场里做得比别人更出色?
股票市场的同质性较低,可供选择的空间更大,但我仍然认为主流股票的市场是高效的。这就是为什么我在 1978 年离开股票研究岗位时,告诉花旗银行,我“除了花一辈子时间在默克和礼来之间做选择之外,什么都愿意干”。我当时相信有效市场,现在依然相信。但我说的“有效”是什么意思?
我说“有效”,指的是“反应迅速”的意思,而不是“正确”。我承认,由于投资者努力评估每一条新信息,资产价格会立即反映出市场对信息重要性的共识看法。但我并不认为共识看法必然正确。2000 年 1 月,雅虎的股价是 237 美元。到 2001 年 4 月,跌到了 11 美元。任何声称市场两次定价都正确的人,简直是异想天开;那两次里至少有一次市场是错的。但这并不意味着许多投资者能够察觉并利用市场的错误。
如果在高效市场中,价格已经反映了共识,那么跟随共识只会让你获得平均回报。要战胜市场,你必须持有独特的、非共识的观点。但由于共识是大多数人所能接近的正确判断,非共识观点不太可能让你比市场更正确(因此也难以帮你战胜市场)。
对我来说,关键在于,尽管更高效的市场常常错误评估资产,但任何一个人——与其他人掌握相同的信息、受同样的心理因素影响——想要持续持有与共识不同且更接近正确的观点,都不是容易的事。这正是主流市场极难战胜的原因——即便它们并不总是正确的。
I believe strongly that some markets are quite efficient, including those for the world's leading stocks and bonds. Take international fixed income, for instance. Here, people try to decide whether British, French or German government bonds are the cheapest at a given time and establish portfolio weightings accordingly. The primary differences between these bonds, it seems to me, relate to their issuing countries' rates of economic growth and inflation. But it's to make allowance for those differences that there exist differential interest rates and floating exchange rates. And aren't those some of the world's most closely watched phenomena, with hundreds of sophisticated financial institutions on both sides of every question? Can any one participant realistically expect to be able to do a superior job in such a market? Stocks are less homogenous, and there's more to choose between them, but I still think the market for popular stocks is efficient. That's the reason why, when I left equity research in 1978, I told Citibank I would "do anything other than spend the rest of my life choosing between Merck and Lilly." I believed in efficient markets then, and I believe in them now. But what do I mean? When I say efficient, I mean it in the sense of "speedy," not "right." I agree that because investors work hard to evaluate every new piece of information, asset prices immediately reflect the consensus view of the information's significance. I do not, however, believe the consensus view is necessarily correct. In January 2000, Yahoo! sold at $237. In April 2001 it was at $11. Anyone who argues that the market was right both times has his head in the clouds; it has to have been wrong on at least one of those occasions. But that doesn't mean many investors were able to detect and act on the market's error. If prices in efficient markets already reflect the consensus, then sharing the consensus view will make you likely to earn just an average return. To beat the market you must hold an idiosyncratic, or non-consensus, view. But because the consensus view is as close to right as most people can get, a non-consensus view is unlikely to make you more right than the market (and thus to help you beat the market). The bottom line for me is that, although the more efficient markets often misvalue assets, its not easy for anyone person – working with the same information as everyone else and subject to the same psychological influences – to consistently hold views that are different from the consensus and closer to being correct. That's what makes the mainstream markets awfully hard to beat – even if they aren't always right. U
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低效——虽然去年我花了很多时间讨论效率,但没有触及低效这个词。这个词我听过被严重误用,通常当作“便宜”的同义词,比如说“去年石油股价格充分,但现在它们真的低效了”。首先,低效不会来去匆匆。市场的低效源于长期的结构性原因,主要与参与者及其基础设施的缺陷有关。其次,“低效”绝不意味着“便宜”(或“昂贵”)。
Inefficiency – Although I spent a lot of time last year discussing efficiency, I didn't touch on inefficiency. This is a word I've heard misused terribly, usually as a synonym for "cheap," as in "the oils were fully priced last year but now they're really inefficient." First of all, inefficiency doesn't come and go in quick bursts. Markets are inefficient for longer-term structural reasons relating primarily to shortcomings on the part of their participants and infrastructure. Second, "inefficient" absolutely does not mean "cheap" (or "dear"). U
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在我看来,效率低下的市场至少具备以下特征之一(而且很可能因为其中一个特征,而同时具备以下所有特征):
To me, an inefficient market is one that is marked by at least one (and probably, as a result, by all) of the following characteristics:
市场价格常常出错。由于获取信息及其分析的途径极不完善,市场价格往往远高于或远低于内在价值。
Market prices are often wrong . Because access to information and the analysis thereof is highly imperfect, market prices are often far above or far below intrinsic values.
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不同资产类别的风险调整后收益可能与其他类别严重脱节。由于资产经常以偏离公允价格的水平被定价,某个资产类别可能提供显著过高(如同免费午餐)或相对其他类别过低的
The risk-adjusted return on one asset class can be far out of line with others . Because assets are often valued at other-than-fair prices, an asset class can deliver a riskadjusted return that is significantly too high (a free lunch) or too low relative to other asset classes.
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一些投资者能够持续跑赢其他投资者。由于存在(a)显著的错误定价,以及(b)参与者在技能、洞察力和信息获取方面的差异,识别错误定价并从中规律性获利是可能的。
Some investors can consistently outperform others . Because of the existence of (a) significant misvaluations and (b) differences between participants in terms of skill, insight and information access, it is possible for misvaluations to be identified and profited from with regularity.
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最后一点,就其含义而言非常重要。低效市场不必然给参与者带来丰厚回报。在我看来,它提供的是原材料——错误定价——让一些人能够凭借不同的技能获胜,另一些人则失败。如果价格可能严重偏离,那就意味着有可能找到便宜货,或者付出过高的代价。在低效市场中,每一个买到便宜货的人,背后都有一个卖得太便宜的人。关于扑克有一句至理名言:“每局牌里都有一个‘鱼’。如果你玩了 45 分钟还没发现谁是‘鱼’,那‘鱼’就是你。”低效市场投资也是如此。
This last point is very important in terms of what it does and does not mean. Inefficient markets do not necessarily give their participants generous returns. Rather, it's my view that they provide the raw material – mispricings – that can allow some people to win and others to lose on the basis of differential skill. If prices can be very wrong, that means it's possible to find bargains or overpay. For every person who gets a good buy in an inefficient market, someone else sells too cheap. One of the great sayings about poker is that, "In every game there's a fish. If you've played for 45 minutes and haven't figured out who the fish is, then it's you." The same is certainly true of inefficient market investing. U
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在不那么有效的市场中,经理人必须具备超凡的个人技能,即“阿尔法”(alpha,见下文)。这其实比在有效市场中重要得多,因为在有效市场中,价格与价值贴合得如此紧密,以至于很难大幅偏离平均水平。关于这一点的有力证据,见下一页表格,出自耶鲁大学戴维·斯文森的《开创性投资组合管理》。
In inefficient markets, then, it's essential that a manager have superior personal skill, or "alpha" (see below). It's actually far more important than in efficient markets, where prices are so well aligned that it's hard to perform far off the average. Good evidence on this subject is found in the table on the next page, from "Pioneering Portfolio Management" by David Swenson of Yale.
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主动管理收益率的分化
揭示机会所在领域
按四分位数划分的资产收益率,截至 1997 年 12 月 31 日的十年期
Dispersion of Active Management Returns Identifies Areas of Opportunity Asset Returns by Quartile, Ten Years Ending December 31, 1997
Asset Class
Asset Class
First Quartile
First Quartile
Median
Median
Third Quartile
Third Quartile
Range
Range
美国固定收益
美国股票
国际股票
房地产
杠杆收购
风险投资
U.S. fixed income U.S. equity Int'l equity Real estate Leveraged buyouts Venture capital
9.7%
19.5
12.6
5.9
23.1
25.1
9.7% 19.5 12.6 5.9 23.1 25.1
9.2%
18.3
11.0
3.9
16.9
12.4
9.2% 18.3 11.0 3.9 16.9 12.4
8.5%
17.0
9.7
1.2
10.1
3.9
8.5% 17.0 9.7 1.2 10.1 3.9
1.2%
2.5
2.9
4.7
13.0
21.2
1.2% 2.5 2.9 4.7 13.0 21.2
正如表格所示,在我认为相对低效的市场(风险投资和杠杆收购)中,投资者表现的第 25 百分位与第 75 百分位之间的差距,远大于更高效的市场(主流股票和债券)。这支持了这样一种观点:在低效市场中,要么(a)价格偏离内在价值的幅度更大,要么(b)投资者技能差异更大,要么(c)这种差异影响更显著,要么(d)上述所有情况并存。无论从哪个角度看,在低效市场中,聘请一位卓越的管理者都更为关键。
As the table shows, the range between the 25 th percentile and the 75 th percentile of investors in what I think are relatively inefficient markets (venture capital and leveraged buyouts) is much broader than it is in more efficient markets (mainstream stocks and bonds). This supports the belief that in inefficient markets, either (a) prices diverge more from intrinsic values, (b) there's more variation among investors in terms of skill, (c) that variation has more impact, or (d) all of the above. Any way you slice it, hiring a superior manager is more crucial in the inefficient markets. P
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回报——阿尔法(alpha)和贝塔(beta)这两个词源于代数方程的基本形式,即:
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Return – The terms alpha and beta are derived from the basic form of an algebraic equation, which is: U
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y = a + bx
因此在投资中,我们说一个投资组合的结果可以通过这个等式预测:
回报 = α +(β × 市场回报)
β 是一个系数,等于投资组合相对于市场回报的捕捉比例。它最好被描述为对市场的“敏感度”或“相对波动性”。一只 S&P 指数基金相对于 S&P 500 指数的 β 为 1.0(也就是说,它会与 S&P 指数同涨同跌)。一只两倍杠杆的 S&P 指数基金,β 为 2.0(即它的反应是市场的两倍)。一个由一半 S&P 指数基金和一半现金组成的投资组合,β 为 0.5。一个防御型股票投资组合的 β 可能在 0.7 左右。
提高你的 β,无论是通过使用杠杆还是偏向更高波动的持仓,当然是试图增加回报的一种方式。按照投资理论,这也是唯一的方式,因为“β × 市场回报”是上述等式中唯一非零的项(稍后详述)。依赖高 β 来提升回报的问题在于,它是完全对称的。它双向起作用,错误时减少的幅度恰如正确时增加的幅度,这意味着除非底层决策正确,否则它不会增加你的预期回报。这正是拉斯维加斯风格的精髓。
y = a + bx Thus in investments we say a portfolio's result can be predicted by the equation: return = alpha + (beta x the market's return) Beta is a coefficient equal to the proportion of the market's return that the portfolio can be expected to capture. It can best be described as "degree of responsiveness" to the market, or "relative volatility." An S&P index fund will have a beta of 1.0 relative to the S&P 500 (that is, it will go up and down at the same rate as the S&P). An S&P index fund leveraged two to one would have a beta of 2.0 (i.e., it will have twice the response). A portfolio consisting of half S&P index fund and half cash will have a beta of .5. A defensive equity portfolio might be expected to have a beta of .7. Turning up your beta, whether through the use of leverage or by emphasizing more volatile holdings, is certainly one way to try to add to your return. Under investment theory it's the only way, since "beta x the market's return" is the only non-zero term in the above equation (more on this later). The trouble with relying on a high beta to enhance your return is that it's entirely symmetrical. It cuts both ways, subtracting as much when it's wrong as it adds when it's right, which means that it does nothing to increase your expected return unless the underlying decisions are right. It epitomizes the Las Vegas
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常说“赌注越大,赢时赢得越多”(但正如我喜欢指出的,输时也输得越多)。
阿尔法(Alpha)是一个变量,等于投资组合经理技能所带来的贡献。正如我在《安全第一》中所写,阿尔法是能够持续从市场波动之外的事物中获利的能力,是在不按比例增加风险的前提下增加回报的能力,是比偶然性所决定的概率更常做出正确判断的能力。其构成要素包括:(a)收集和分析信息,(b)辨别哪些因素对决定未来价值最为关键,(c)抵御市场躁郁症般的波动,这些方面的卓越表现。
阿尔法正是市场有效时所缺失的东西。但正如我相信存在一些相对有效的市场,我也确信拥有阿尔法的人确实存在,同时也存在效率较低的市场,能让阿尔法得以施展。
必须认识到,投资技能并非平均分配——投资世界并非民主或平等的。这就是为什么花旗银行老板彼得·弗米利(Peter Vermilye)——他引导我进入可转换债券和高收益债券领域——说只有顶尖的 10% 分析师才有实际贡献。这也是为什么我对那些以人数多少来描述自身优势的投资管理公司评价甚低;一支平庸分析师组成的大军对你毫无用处。
那是因为,在我看来,阿尔法最好被理解为“差异化优势”,即他人不具备的技能。阿尔法不是知道某事,而是知道别人不知道的事。如果其他人也共享某份知识,它就不构成优势。考虑到市场价格体现了投资者的共识——而投资者平均而言知道你所知道的东西——这当然不会帮你跑赢市场。
saying that "the more you bet, the more you win when you win" (but also, as I like to point out, the more you lose when you lose). Alpha is a variable equal to the contribution resulting from the skill of the portfolio manager. As I wrote in "Safety First," alpha is the ability to profit consistently from things other than the movements of the market, to add to return without adding proportionately to risk, and to be right more often than is called for by chance. Examples of its ingredients include superiority in (a) collecting and analyzing information, (b) discerning which factors are most important in determining future value, and (c) resisting the market's manic-depressive fluctuations. Alpha is what's lacking when a market is efficient. But just as I believe there are some relatively efficient markets, I'm also sure people with alpha exist, as well as less efficient markets where it can be put to good use. It's essential to recognize that investment skill isn't distributed evenly – that the investment world isn't democratic or egalitarian. That's why Peter Vermilye, the Citibank boss who steered me toward convertibles and high yield bonds, says only the top 10% of analysts contribute anything. It's also why I think so little of investment management firms that describe their edge in terms of head count; an army of average analysts will do you no good. That's because, in my view, alpha is best thought of as " differential advantage," or skill that others don't possess. Alpha isn't knowing something, it's knowing something others don't know. If everyone else shares a bit of knowledge, it provides no advantage. It certainly won't help you beat the market, given that the market price embodies the consensus view of investors – who on average know what you know. U
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Alpha 完全是个人化的东西。它因人而异,堪称一门艺术。它是高人一等的洞察力;有些人就是比别人“更懂”。其中有些人是机械式的量化派,另一些人则完全靠直觉。在我认识的最优秀投资者身上,努力是共同点,但单靠努力绝对不足以解释他们出类拔萃的表现。对毫无技能的人(比如乱掷飞镖的人)来说,Alpha 等于零。而沃伦·巴菲特,即便在一个大多数人认为有效的市场里,似乎也拥有大量 Alpha。如果你判断错误的次数多于正确的次数,那你的 Alpha 可能为负。一个总是犯错的人会积累大量负 Alpha,但认识他却是件大好事(因为你只要反着他说的话做,就能永远正确)。人人都知道,投资理论的基石之一就是根本不存在 Alpha 这回事……
显然,这正是有效市场假说的基础。市场比任何投资者都更正确。没有哪个投资者比另一个更强。没人能持续跑赢大盘。学术界人士把那些表现优异的轶事证据归因于运气或试错期太短,一概不予采信。
Alpha is entirely personal. It's idiosyncratic, an art form. It's superior insight; some people just "get it" better than others. Some of them are mechanistic quants; others are entirely intuitive. Hard work is a common thread among the best investors I know, but hard work alone is absolutely insufficient to explain their superior performance. Alpha is zero for someone with no skill (i.e., a dart thrower). Warren Buffett, on the other hand, seems to have lots of alpha – even in a market most people think of as efficient. It's possible to have negative alpha if you're wrong more often than not. Someone who's always wrong would have lots of negative alpha, but he'd be a great guy to know (since you could be right all the time by doing the opposite of what he says). Everyone knows it's a cornerstone of investment theory that there's no such thing as alpha . . . Clearly this underlies the Efficient Market Hypothesis. The market is more right than any investor. No investor is better than any other. No one is capable of consistently outperforming. Anecdotal evidence of superior performance is dismissed by academicians who attribute it to luck or a too-short trial period.
2001 年,橡树资本管理有限合伙公司(Oaktree Capital Management, L.P.)
2001 Oaktree Capital Management, L.P.
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……但这其中却有点自相矛盾的味道。尽管成千上万的人指望靠主动投资管理谋生,但传统投资思想的大部分根基,却是建立在“阿尔法极为有限”这一认知之上的(尽管从业者不会这么直说)。
我为何这么说?多数投资者声称自己能跑赢市场——也就是说,能比普通投资者看得更清、判断更准、理解更深——靠的是过人的聪明和勤奋。谁不觉得自己能战胜市场?但实际上,大量实际操作——连橡树资本也不例外——都在微妙地承认:知道得更多的能力——你想想看,阿尔法在很大程度上不就是这个吗——是相当有限的。
人们普遍认为,如果某位投资者的组合高度集中,那风险就很大。但这一假设的前提是他看不清未来。如果他看得清,那么低度分散就是绝对安全的。事实上,如果他的预见力完美无缺,那么最安全的组合反而只该持有一项资产,因为那是他最为看好的那只(而且,既然他能预见未来,他当然是对的)。因此,分散投资——即使在“我懂”派投资中也被广泛采用——其实是在默认:投资者有太多东西是不知道的。
投资者对流动性的强烈偏好,也是对这一局限性的另一重默认。连那些“我懂”派投资者——他们在买入时认定自己是对的——也坚持要流动性,因为他们知道,自己很有可能会错,到时候得赶紧撤退。可你越是能看清未来,犯错的概率就越低,退出困难的风险也就越小。
所以,说到底,不仅是投资理论,连大量日常实践都围绕着一个共识来构建:阿尔法——也就是技能和预见力——是稀缺品。
风险——投资者必须考虑风险,这一点至关重要。自我踏入投资领域以来,收益越来越被要求按风险调整后的口径来评估。人人都知道,如果两个组合五年里每年回报 8%,这两位经理人做的投资工作不一定同样出色。如果一位靠的是国库券,另一位靠的是新兴市场股票,那么第一位经理人几乎肯定干得更好——因为他以低得多的风险赚到了同样的回报。这才是真正的附加价值,跟用相同或更低风险赚到更高回报是一回事。所以,要判断一位经理人干得有多好,你就得清楚他承担了多少风险。
. . . but there's something of an oxymoron afoot. Even though thousands of people expect to make a living from active investment management, much of traditional investment thinking is built on the realization that alpha is severely limited (even though the practitioners don't state it that way). Why do I say that? Most investors claim they can outperform the market – that is, can see, assess and understand better than the average investor – because of superior intelligence and hard work. Doesn't everyone think he can beat the market? But much of what's actually practiced, even by Oaktree, subtly acknowledges that the ability to know more – and if you think of it, that's a lot of what alpha really is – is quite limited. It's a common assumption that if an investor's portfolios are highly concentrated, they're risky. But that assumes he can't see the future. If he could, it would be perfectly safe to have a low level of diversification. In fact, if his foresight were perfect, then the safest portfolio would hold only one asset, because that's the one he would think of most highly (and, since he could see the future, he would of course be right). Thus diversification, which is widely practiced even in the "I know" school of investing, represents a tacit acknowledgement that there's a lot that investors don't know. Investors' strong preference for liquidity is another indicator that this limitation is accepted. Even the "I know" investors, who buy on the assumption they're right, insist on liquidity – because they know there's a good chance they'll be wrong and need to beat a retreat. But the more you can see the future, the less likely you'll be wrong, and the less risk there is that exiting could be difficult. In reality, then, not just investment theory, but also a great deal of everyday practice, is built around the acknowledgement that alpha – skill and foresight – is a scarce commodity. Risk – It's essential that investors consider risk. In the time since I entered the investment field, return has increasingly come to be evaluated in risk-adjusted terms. Everyone knows that if two portfolios return 8% a year for five years, the two managers didn't necessarily do an equally good job of investing. If one did it with T-bills and the other with emerging market stocks, the first manager almost certainly did a better job – since he earned the same return with far less risk. That's real added value, just like earning more return with the same or less risk. To know how good a job a manager did, then, you have to have a good idea how much risk he took. U
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但我认为,风险或许正是理论与实践诸多方面偏离正确最远的领域。投资理论教你第一课,也是实践中最为广泛认同的假设之一,便是“波动性等于风险”。这一前提支撑着大量投资组合理论、资产配置、投资组合优化及绩效评估。但它究竟有何可取之处呢?
Yet I think risk may be the area where both theory and many aspects of practice are furthest from right. The first thing you learn in investment theory, and one of the most widely agreed-on assumptions in practice, is that "volatility equals risk." This premise underlies a great deal of portfolio theory, asset allocation, portfolio optimization and performance assessment. But what are its merits?
2001 年橡树资本管理有限合伙公司
2001 Oaktree Capital Management, L.P.
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我相信,上世纪五六十年代的学者们之所以接受波动性作为投资风险的衡量标准,是被它的两大优点所吸引:(a)绝对性和(b)可量化性。他们能精确地告诉你某只股票或某个投资组合过去回报的标准差,因此只需稍作外推,就能预测未来的表现。
我想提出一些思考风险的其他方式,但(a)这些方式会因人而异、因情境而异,并且/或者(b)不易量化。因此,它们无法让你断言某项资产或投资组合比另一项风险更高(除非在特定的应用场景下)。你甚至无法说明某项资产或投资组合过去的风险有多大。
什么是风险?首先,我不认为风险等同于波动性。其次,风险的标志因资产类别而异。
在橡树资本,当我们考虑将一项资产纳入投资组合时,我们会问:所涉及的风险是否可承受(即在我们从客户那里获得授权范围内),并且是否可能被预期回报所抵消。我们所说的风险,是指损失客户资金的可能性。
在高收益债券中,我们关注的是违约风险以及可能无法收回的本金数额。在不良债务中,我们思考的是公司资产是否会比我们想象的更不值钱,或者重组是否会对我们不利。在可转换债券和新兴市场股票中,我们担心股价下跌的可能性,以及我们的保护措施能否成功隔离风险。
我们不考虑波动性。我们的资金要么锁定在封闭式基金中,要么建立在长期关系之上,我们只关心最终结果——也许是多年以后——是正还是负,以及幅度有多大。我们认为这正是客户付钱让我们做的事情。
但我们并不声称这种风险处理方法可以被量化或进行数值操作。布鲁斯·卡什去年六月买入康赛可债券时,可能无法量化其风险。理查德·马森和马特·巴雷特在亏损概率上可能不会同意他的看法,甚至彼此意见相左。他们最终确定的任何数字,可能都无法以能与风险等同的形式呈现。即使是今天,一年之后,债券已经卖出,我们仍然无法量化所承担的风险。它是一个概念、一种感觉、一个担忧……但不是数字。
这可能是思考风险的正确方式——我们确实是这么做的——但对“量化专家”来说完全行不通。他无法表述我们投资组合的风险,或风险调整后回报,也无法判断我们的表现是优是劣。
一笔投资会亏钱吗?一个养老基金会无法达到精算假设的回报吗?一只捐赠基金会不会难以覆盖其支出率?一个退休人员会不会入不敷出?一位经理会不会失去客户?这些才是我们所认为的真正风险——危险所在。
I believe the academicians of the 1950s and '60s were influenced to accept volatility as the measure of investment risk by its two outstanding virtues: it is (a) absolute and (b) quantifiable. They can tell you precisely what the standard deviation of a stock or a portfolio's return was in the past, and thus it only takes a little extrapolation to project what it's going to be in the future. I will suggest some other ways to think about risk, but (a) they will vary from person to person and from situation to situation, and/or (b) they will not be easily quantified. Thus they won't permit you to say that one asset or portfolio would be riskier than another (other than possibly in a given application). You won't even be able to say how risky an asset or portfolio was in the past. What is risk? First of all, I don't think risk is synonymous with volatility. And second, the indicia of risk vary by asset class. At Oaktree, when we think about adding an asset to a portfolio, we ask whether the risk entailed is tolerable (i.e., within our charter from our clients) and offset by the likely return. And by risk we mean the chance of losing our clients' money. In high yield bonds we concentrate on the risk of default and how much principal would likely be unrecoverable. In distressed debt we wonder whether the company's assets will turn out to be worth less than we think or the reorganization will go against us. In convertibles and emerging market equities we worry about the chance a stock will decline and the likelihood that our protective efforts will fail to insulate us. We do not think about volatility. With our capital in either locked-up funds or long-term relationships, we worry only about whether the ultimate result, perhaps years down the road, will be positive or negative, and by how much. We think this is what our clients pay us to do. But we make no claim that this approach to risk is subject to quantification or numerical manipulation. Bruce Karsh probably couldn't have quantified the riskiness of Conseco bonds at the time we bought them last June. Richard Masson and Matt Barrett probably wouldn't have agreed with him, or with each other, on the probability of loss. Any figure they settled on probably wouldn't have been in a form that could be equated with risk. And even today, a year later and after having sold the bonds, we still can't quantify the risk we took. It's a concept, a notion, a worry . . . but not a number. This might be the right way to think about risk – it's certainly how we do it – but it wouldn't work at all for a "quant." He'd have no way to state our portfolio's risk, or its risk-adjusted return, or tell whether our performance was superior or inferior. Will an investment lose money? Will a pension fund fail to earn its actuarial assumption? Will an endowment be unable to cover its spending rate? Will a retiree have less than he needs to live on? Will a manager lose an account? These are the risks – the perils – that we think matter.
2001 年橡树资本管理有限合伙公司
2001 Oaktree Capital Management, L.P.
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大多数养老基金拥有非常长的时间跨度,而大学捐赠基金的时间跨度理论上甚至是无限的。季度性的波动回报对它们而言,不像对勉强维生的退休人员那样,构成有意义的风险来源。但一旦你认识到,某个特定投资组合对一位投资者是危险的,对另一位却不是,就不存在一个唯一的数字来衡量其绝对风险。既然如此,又怎能谈论它的风险,或是其风险调整后回报呢?
相关性——将证券组合成投资组合时,需要考虑的最后一个分析要素,是它们之间的关联程度,即相关性。如上所述,对于能预知未来的人而言,单一资产组合是最优选择。持有多种资产的主要原因在于分散化。但分散化最核心的价值——防范灾难性错误的保护——如果底层资产对环境变化反应一致、同向波动,其作用便荡然无存。
Most pension funds have a very long time horizon, and for a university endowment it's theoretically infinite. Volatile quarterly returns wouldn't be a meaningful source of risk for them as they would be for a retiree scraping by. But once you say a given portfolio is risky for one investor but not another, there ceases to be a unique number that measures its absolute riskiness. In that case, how can you talk about its risk, or its risk-adjusted return? Correlation – The final analytical element to be considered when assembling securities into portfolios is their degree of connectedness, or correlation. As discussed above, a one-asset portfolio would be optimal for someone who can see the future. The main reason for holding more than one asset is diversification. But the principal virtue of diversification, protection from catastrophic error, is wiped out if the underlying assets will react the same to environmental change and move together.
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所以,单看资产本身的回报和风险是不够的,我们必须理解相关性。就算能分别估算两项资产的潜力,如果不知道它们彼此会如何联动,也无法预知把两者组合起来后投资组合会怎么走。同行业的两只股票可能高度相关,但产品直接竞争的两家公司未必如此(也就是说,谁赢,另一家大概率就得输)。
假设有两项资产,潜在回报和风险都很高。由这两项构成的组合,如果二者相关,风险就高;如果不相关,风险就低。所以,加入一项不相关的高风险资产,反而能降低整个组合的风险。这个认知彻底改变了投资界,让风险厌恶型投资者也能持有高回报、高风险的资产,前提是这些资产与组合里其他部分不相关。橡树资本能走到今天,很大程度上正是得益于对资产组合行为方式的理解。
跟踪误差,最近越来越受关注,它指的是特定类型的一种关联:组合与基准之间的关联。客户越来越频繁地追问经理人过去的跟踪误差,并在聘用后持续监控。客户聘请经理人,是让其在组合里扮演特定角色,希望确保他们能照做不误。比如,客户考虑要不要把高收益债纳入组合时,可能会用所罗门现金支付指数当高收益债部分的代理指标,来模拟组合的表现。然后,若客户决定聘请经理人,就希望确保经理人能紧贴所罗门指数(当然,同时还得跑赢它!)
所以,客户有理由希望跟踪误差低。但仔细想想,跟踪误差的两个主要来源,一是对指数内证券的超配或低配,二是纳入指数之外的证券。因此,跟踪误差显然有可能低过头;指数基金的跟踪误差是零,但客户雇主动型经理人,要的不是这个。于是,我们就有客户盯着我们的跟踪误差,太低时反而抱怨,因为他们想看到主动下注的动作。
Thus it's not enough to be able to estimate return and risk in isolation; we must understand correlation. Even if we can estimate the separate potential of two assets, we cannot know how a portfolio combining them will behave unless we know how they will move relative to each other. Two stocks in the same industry may be highly correlated, but two companies whose products compete directly may not (that is, whichever one wins, the other is likely to lose). Let's say there are two assets with high prospective return and risk. A portfolio consisting of the two can have high risk if they are correlated but low risk if they are not. Thus adding an uncorrelated, high-risk asset can reduce the overall riskiness of a portfolio. This understanding revolutionized investing by enabling risk-averse investors to hold high-return, high-risk assets as long as they are uncorrelated with the rest of their portfolio. Certainly Oaktree owes much of its very existence to the understanding of how assets behave in combination. Tracking error, which lately has been of increased interest, refers to a specific type of connectedness: that between a portfolio and a benchmark. More and more, clients are asking about managers' tracking error in the past and monitoring it after hiring them. A client hires managers to play specific roles in its portfolio, and it wants to be sure they will do so. In considering whether to include high yield bonds in its portfolio, for example, the client may model the performance of the portfolio incorporating the Salomon Cash-Pay Index as a proxy for the high yield bond component. Then if the client hires a manager, it wants to be sure the manager will track the Salomon Index closely (of course while outperforming!) Thus clients have reason to want low tracking error. But if you think about it, the two principal sources of tracking error are (a) over- and under-weightings of the securities in the index and (b) inclusion of off-index securities. So it's obviously possible for tracking error to be too low; an index fund would have zero tracking error, but that's not what clients hire active managers to create. Thus we have a client who monitors our tracking error and complains when it's too low, because they want to see active bets being made.
2001 年橡树资本管理公司(Oaktree Capital Management, L.P.)
2001 Oaktree Capital Management, L.P.
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最后一点说明了我认为理论在我们这一行应当扮演的角色。简而言之,理论应当为我们的决策提供参考,而不是主导决策。
This last point illustrates what I think should be the role of theory in our industry. In short, I think, theory should inform our decisions but not dominate them. U
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如果我们完全无视理论,就可能犯下大错。我们会自欺欺人地以为,自己能比旁人知道得更多,能在竞争激烈的市场中屡屡胜出。我们会为了收益买入证券,却忽视了其中的风险。我们会买入五十只相互关联的证券,还误以为自己已经分散了风险。每当想到无视理论所带来的后果,我就会回想起 1970 年,那时我的同事们指望股市每年带来 12% 的回报,其理由简单得令人不安:如果通过指数化投资,轻松就能复制历史上 10% 的回报率,那么再多费点劲,多加几个百分点岂不是轻而易举。
但全盘照搬理论,又可能让我们把决策权交给电脑,从而错过那些能干之人的贡献。这里有个画面:一位坚信有效市场的金融教授,带着学生散步。学生问:“地上那张是不是 10 美元钞票?”“不可能,那不会是 10 美元钞票,”教授答道,“要是的话,早就有人捡走了。”教授走开了,学生捡起钞票,去喝了杯啤酒。
那么,我们该如何在两者间取得平衡?靠的是有见识的常识。在芝加哥,我和詹姆斯·洛里教授共度了一个精彩的学期。学生们喜欢他那门充满轶事的课程,我们昵称它为“洛里讲古”,还喜欢课上请来的活跃投资者嘉宾。信奉理论的纯粹主义者或许会对这门课嗤之以鼻,但正是这门课启发了我,让我把惠顿学到的实务功底和芝加哥的理论融会贯通,而不是死守其中一方。
毕业一年后,我和吉姆·洛里共进午餐,我抛开理论话题,请教他实际会如何管理投资组合。他的建议简单,既有理论依据,又切合实际:“核心部分用指数化,外围部分则狠狠下功夫管理。”
If we entirely ignore theory, we can make big mistakes. We can fool ourselves into thinking it's possible to know more than everyone else and regularly beat heavily populated markets. We can buy securities for their returns but ignore their risk. We can buy fifty correlated securities and mistakenly think we've diversified. When I think of the impact of being blind to theory, I flash back to 1970 and the frighteningly simplistic rationale behind my colleagues' expectation of 12% a year from stocks: if they could emulate the historic 10% return with ease through indexing, it should be a snap to add a couple of percent with just a little effort. But swallowing theory whole can make us turn the process over to a computer and miss out on the contribution skillful individuals can make. The image here is of the efficient-market-believing finance professor who takes a walk with a student. "Isn't that a $10 bill lying on the ground?" asks the student. "No, it can't be a $10 bill," answers the professor. "If it were, someone would have picked it up by now." The professor walks away, and the student picks it up and has a beer. So how do we balance the two? By applying informed common sense. At Chicago, I spent a wonderful semester with Professor James Lorie. Students loved his anecdotefilled course, which we nicknamed "Lorie's Stories," and its visits from active investors. True-believing theorists may have sneered at it, but it was this class that inspired me to integrate my practical Wharton foundation and the Chicago theory, rather than stick exclusively to either one. A year after graduating, I had lunch with Jim Lorie and asked – off the theoretical record – how he would manage a portfolio. His simple advice was informed by theory but realistic: "I would index the core and manage the hell out of the periphery." *
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我投资管理生涯的关键转折点,始于我认定在低效市场中,勤奋与技能最能收获回报。理论为这一判断提供了指引,使我免于在其他领域虚掷光阴;但唯有理解理论的局限,我才未全然接受反对主动管理的论点。理论与实践须如此平衡,显然,仅凭其一,皆不足为训。
The key turning point in my investment management career came when I concluded that hard work and skill would pay off best in inefficient markets. Theory informed that decision and prevented me from wasting my time elsewhere, but it took an understanding of the limits of the theory to keep me from completely accepting the arguments against active management. Theory and practice have to be balanced in this way. Certainly neither alone is enough.
July 11, 2001
July 11, 2001
2001 年橡树资本管理公司(Oaktree Capital Management, L.P.)
2001 Oaktree Capital Management, L.P.
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