In his 2006 research report Painting By Numbers: An Ode To Quant (via The Hedge Fund Journal) James Montier presents a compelling argument for a quantitative approach to investing. Montier’s thesis is that simple statistical or quantitative models consistently outperform expert judgements. This phenomenon continues even when the experts are provided with the models’ predictions. Montier argues that the models outperform because humans are overconfident, biased, and unable or unwilling to change.
Montier makes his argument via a series of examples drawn from fields other than investment. The first example he gives, which he describes as a “classic in the field” and which succinctly demonstrates the two important elements of his thesis, is the diagnosis of patients as either neurotic or psychotic. The distinction is as follows: a psychotic patient “has lost touch with the external world” whereas a neurotic patient “is in touch with the external world but suffering from internal emotional distress, which may be immobilising.” According to Montier, the standard test to distinguish between neurosis or psychosis is the Minnesota Multiphasic Personality Inventory or MMPI:
In 1968, Lewis Goldberg1 obtained access to more than 1000 patients’ MMPI test responses and final diagnoses as neurotic or psychotic. He developed a simple statistical formula, based on 10 MMPI scores, to predict the final diagnosis. His model was roughly 70% accurate when applied out of sample. Goldberg then gave MMPI scores to experienced and inexperienced clinical psychologists and asked them to diagnose the patient. As Fig.1 shows, the simple quant rule significantly outperformed even the best of the psychologists.
Even when the results of the rules’ predictions were made available to the psychologists, they still underperformed the model. This is a very important point: much as we all like to think we can add something to the quant model output, the truth is that very often quant models represent a ceiling in performance (from which we detract) rather than a floor (to which we can add).
The MMPI example illustrates the two important points of Montier’s thesis:
- The simple statistical model outperforms the judgements of the best experts.
- The simple statistical model outperforms the judgements of the best experts, even when those experts are given access to the simple statistical model.
Montier goes on to give diverse examples of the application of his theory, ranging from the detection of brain damage, the interview process to admit students to university, the likelihood of a criminal to re-offend, the selection of “good” and “bad” vintages of Bordeaux wine, and the buying decisions of purchasing managers. He then discusses some “meta-analysis” of studies to demonstrate that “the range of evidence I’ve presented here is not somehow a biased selection designed to prove my point:”
Grove et al consider an impressive 136 studies of simple quant models versus human judgements. The range of studies covered areas as diverse as criminal recidivism to occupational choice, diagnosis of heart attacks to academic performance. Across these studies 64 clearly favoured the model, 64 showed approximately the same result between the model and human judgement, and a mere 8 studies found in favour of human judgements. All of these eight shared one trait in common; the humans had more information than the quant models. If the quant models had the same information it is highly likely they would have outperformed.
As Paul Meehl (one of the founding fathers of the importance of quant models versus human judgements) wrote: There is no controversy in social science which shows such a large body of qualitatively diverse studies coming out so uniformly in the same direction as this one… predicting everything from the outcomes of football games to the diagnosis of liver disease and when you can hardly come up with a half a dozen studies showing even a weak tendencyin favour of the clinician, it is time to draw a practical conclusion.
Why not investing?
Montier says that, within the world of investing, the quantitative approach is “far from common,” and, where it does exist, the practitioners tend to be “rocket scientist uber-geeks,” the implication being that they would not employ a simple model. So why isn’t quantitative investing more common? According to Montier, the “most likely answer is overconfidence.”
We all think that we know better than simple models. The key to the quant model’s performance is that it has a known error rate while our error rates are unknown.
The most common response to these findings is to argue that surely a fund manager should be able to use quant as an input, with the flexibility to override the model when required. However, as mentioned above, the evidence suggests that quant models tend to act as a ceiling rather than a floor for our behaviour. Additionally there is plenty of evidence to suggest that we tend to overweight our own opinions and experiences against statistical evidence.
Montier provides the following example is support of his contention that we tend to prefer our own views to statistical evidence:
For instance, Yaniv and Kleinberger11 have a clever experiment based on general knowledge questions such as: In which year were the Dead Sea scrolls discovered?
Participants are asked to give a point estimate and a 95% confidence interval. Having done this they are then presented with an advisor’s suggested answer, and asked for their final best estimate and rate of estimates. Fig.7 shows the average mean absolute error in years for the original answer and the final answer. The final answer is more accurate than the initial guess.
The most logical way of combining your view with that of the advisor is to give equal weight to each answer. However, participants were not doing this (they would have been even more accurate if they had done so). Instead they were putting a 71% weight on their own answer. In over half the trials the weight on their own view was actually 90-100%! This represents egocentric discounting – the weighing of one’s own opinions as much more important than another’s view.
Similarly, Simonsohn et al12 showed that in a series of experiments direct experience is frequently much more heavily weighted than general experience, even if the information is equally relevant and objective. They note, “If people use their direct experience to assess the likelihood of events, they are likely to overweight the importance of unlikely events that have occurred to them, and to underestimate the importance of those that have not”. In fact, in one of their experiments, Simonsohn et al found that personal experience was weighted twice as heavily as vicarious experience! This is an uncannily close estimate to that obtained by Yaniv and Kleinberger in an entirely different setting.
It is worth noting that Montier identifies LSV Asset Management and Fuller & Thaler Asset Management as being ”fairly normal” quantitative funds (as opposed to being “rocket scientist uber-geeks”) with “admirable track records in terms of outperformance.” You might recognize the names: “LSV” stands for Lakonishok, Shleifer, and Vishny, authors of the landmark Contrarian Investment, Extrapolation and Risk paper, and the “Thaler” in Fuller & Thaler is Richard H. Thaler, co-author of Further Evidence on Investor Overreaction and Stock Market Seasonality, both papers I’m wont to cite. I’m not entirely sure what strategies LSV and Fuller & Thaler pursue, wrapped as they are in the cloaks of “behavioural finance,” but judging from those two papers, I’d say it’s a fair bet that they are both pursuing value-based strategies.
It might be a while before we see a purely quantitative value fund, or at least a fund that acknowledges that it is one. As Montier notes:
We find it ‘easy’ to understand the idea of analysts searching for value, and fund managers rooting out hidden opportunities. However, selling a quant model will be much harder. The term ‘black box’ will be bandied around in a highly pejorative way. Consultants may question why they are employing you at all, if ‘all’ you do is turn up and run the model and then walk away again.
It is for reasons like these that quant investing is likely to remain a fringe activity, no matter how successful it may be.
Montier’s now at GMO, and has produced a new research report called Ten Lessons (Not?) Learnt (via Trader’s Narrative).
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