A topic I have changed my mind on during my career is concentration in funds. I used to be strongly of the view that it was only worth taking active investment positions if they came with high conviction – usually in the form of concentrated positioning – otherwise, what’s the point? Although I came to realise I was wrong about this, I am aware that many people far smarter than me remain advocates of this type of approach. Why do I think it is a problem when they don’t?

Fund concentration is not the easiest concept to define. There are obvious examples such as very focused equity portfolios with large weightings in individual companies, but there is more to it than that. Concentration doesn’t have to be about position sizes in stocks, it can come through an extreme sensitivity to a certain theme, concept or risk factor. It is about our exposure to specific and singular points of failure.  Could one thing go wrong and lead to disaster?

The key concept to consider when thinking about the risk of concentrated funds is ergodicity. This is a horribly impenetrable term, but at its core is the idea that there can be a difference between the average result produced by a group of people carrying out an activity, and the average result of an individual doing the same thing through time.

Let’s use some simple examples.

Rolling a dice 20 times is an example of an ergodic system. It doesn’t matter if 20 people roll the dice once each, or an individual rolls the dice 20 times. The expected average result of both approaches is identical.   

Conversely, home insurance is a non-ergodic system. At a group level the expected average value for buyers of home insurance is negative (insurance companies should make money from writing policies). So, why do we bother purchasing it? Because, if we do not, we expose ourselves to the potential for catastrophic losses. The experience of certain individuals through time will be dramatically different to the small loss expected at the average group level.

Investing is non-ergodic. Our focus should therefore be on our individual experience across time (not the average of a group); this means being aware of how wide the potential range of outcomes are and the risk of ruin.

In concentrated funds, the prospect of suffering irrecoverable losses at some point in the future is too often unnecessarily high.

‘Risk is not knowing what you are invested in’

One of the most common arguments made by advocates of running very concentrated equity portfolios is that it is an inherently lower risk pursuit because we can know far more about a narrow list of companies than a long list. If we have a 10 stock portfolio we can grasp the companies in a level of detail that is just not possible if we hold 100 stocks, and this depth of understanding means that our risk is reduced. The first part of this is right, the second part is wrong.

The problem, I think, stems from the fact that there are two types of uncertainty – epistemic and aleatoric. Epistemic uncertainty is the type that can be reduced by the acquisition of more data and knowledge. Here the idea of portfolio concentration lowering risk makes sense. Conversely, aleatoric uncertainty is inherent in the system; it is the randomness and unpredictability that cannot be reduced. It doesn’t matter how well we know a company or an investment, we are inescapably exposed to this. The more concentrated we are, the more vulnerable we are to unforeseeable events.

While I think a neglect of aleatoric uncertainty is at the heart of unnecessarily concentrated portfolios, there are other issues at play. Overconfidence is likely to be a key feature. we may be aware that the range of outcomes from a concentrated approach is wide, but that may be desirous to us because we believe that our skill skews the results towards the positive side of the ledger. Given our ability to fool ourselves and the aforementioned chaotic nature of the system, this seems to be a dangerous assumption to make.  

Unfortunately, there is also an incentive alignment problem. A wide range of potential outcomes from an investment strategy becomes very appealing if we benefit from the upside but someone else bears the downside. This asymmetry is inevitably one of the reasons why high-profile macro hedge funds so often seem to be swinging for the fence with concentrated views. The often-severe downside of the negative outcomes are borne primarily by the client (a situation no doubt exacerbated when a hedge fund manager is already exceptionally wealthy).

Running a very concentrated investment strategy places an incredibly heavy onus on being right and also leaves us acutely vulnerable to unforeseen events unfolding that can have profoundly negative consequences. Exposing ourselves to such risks wilfully seems imprudent and unnecessary.

Investors are likely to overestimate how much they know, and underestimate how much they cannot know.

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– Being wary of concentration does not mean increasing levels of diversification are always beneficial. There is a balance to strike.

– It feels important to note that the risk of concentrated strategies can be diversified by combining them, but we should still consider what the concentration levels say about the investor who is willing to adopt such an approach.

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My first book has been published. The Intelligent Fund Investor explores the beliefs and behaviours that lead investors astray, and shows how we can make better decisions. You can get a copy here (UK) or here (US).