In a world where investors are increasingly being encouraged to react and trade (typically not for their benefit), doing nothing can often prove to be sage investment advice. In a recent paper, Hendrik Bessembinder analysed the performance of “do nothing” portfolios, and shows that even if we are doing very little, the results we achieve will be heavily influenced by the small choices we make.
To run his analysis, Bessembinder created a series of “do nothing” portfolios from the constituents of the S&P 500 at the end of each year from 1970. The portfolios are “do nothing” as there are no trades after the portfolio is formed, apart from dividend reinvestment. If a stock is delisted, the proceeds are held in cash for the remainder of the period. The underlying idea is to understand what would happen if we simply bought a selection of stocks on a certain day and then ‘left them in the drawer’. It is not quite a “do nothing” approach, but it gets pretty close.
I don’t want to simply repeat the findings of Bessembinder’s paper, and I would recommend reading it directly, but I thought I would draw out what I thought were the most interesting aspects of the results:
Rebalancing Matters
Over the full 55 year sample, an equally weighted “do nothing” portfolio (holding all available stocks at the same position size) grew from $1 to $678, while a value weighted approach (the typical index market cap structure) grew to only $361. This is a huge advantage for an equal weighted over a market cap strategy. Bessembinder suggests that this could be due to a ‘small cap effect’ boosting returns for the equal weighted approach. While this might explain some of the difference, I am doubtful that this is responsible for the entire gap – the underlying constituents are S&P 500 companies, so nothing is genuinely ‘small’. I think the differential is more likely due to rebalancing.
In the example above, the portfolios are not quite “do nothing” as they are rebalanced back to target weights at the end of each year. The impact of rebalancing is far more significant for an equal weighted approach where target allocations are fixed, unlike market cap where they move with performance. The paper also shows the impact of extending the rebalancing window to only every ten years. Here the gap between the returns of the equal weighted portfolio and the market cap portfolio collapses – the end value of equal weight is $387 and for market cap $342.
It appears that a substantial portion of the return advantage for an equal weighted “do nothing” approach came from a premium attributable to harvesting the volatility of the underlying assets over time. That is selling down stocks after periods of outperformance and vice-versa. Of course, a rebalancing effect does not only stem from an equally weighted portfolio, it comes from any strategy where the weightings of the holdings are not linked to the underlying price of the assets – equal weighting is simply one example.
Even when we wish to take a hands off approach to our investment strategy, there are seemingly innocuous decisions that can have a profound impact on outcomes.
The Two Types of Market Timing
I write frequently about the futility of market timing. I don’t think that people can predict the short-term movements of financial markets, and I wish they wouldn’t try. There is, however, another type of market timing that is far less deliberate, but can be even more influential – our starting point.
Although not a direct angle of the paper, Bessembinder’s work does show how the apparent efficacy of any given strategy is heavily dependent on the period over which we observe its returns. One of the approaches analysed is simply to buy the largest stock in the index and then “do nothing”. The fortunes of this admittedly extreme method depend entirely on when you start.
If you did nothing but owned Microsoft from 1999 you would have lost 33% over the subsequent decade, but if you had applied the same strategy in 2016 you would have held Apple and gained 1,046% over the next ten years.
There are two important takeaways from this (aside from – please don’t invest your entire portfolio in a single stock). First, is that our investment outcomes will be influenced by the point in time when we invest – this will apply to a single stock or a highly diversified 60/40 portfolio. A great deal of this will be down to chance. Second, the more concentrated your investment strategy, the more beholden you become to the point in time you invest, because as concentration increases, so does the range of outcomes. Being diversified mitigates, but does not remove, timing risk.
The Concentration Conundrum
You may recall Hendrik Bessembinder from his previous paper which looked at how concentrated equity market returns were over time – just 46 firms accounted for over half of the $91trn in net wealth created over the course of a century, and the median buy and hold return across individual stocks was negative. When contrasted with Bessembinder’s new paper, this creates something of a puzzle.
His research on concentrated stock market returns implicitly supports taking a diversified, market cap-based approach to equity investing – this ensures that you have an increasing exposure to the companies that matter over time. This new paper, however, highlights the positive impact of an equal weighted approach, which benefits from harvesting a rebalancing premium from volatile equity markets, explicitly cutting the winners and bringing them back to their initial size.
So, which is better?
It is important to note that the samples used for the two papers are different – his work on concentration incorporates a far greater number of companies assessed over a longer horizon. Although this means that the results of the two studies are not directly comparable, that distinction also brings us to the answer – it depends. The consequence of running winners rather than rebalancing is dependent on the prevailing environment. If performance over an extended spell is skewed towards a select group of large winners allowing concentration to build can pay-off, if this is not the case, the rebalancing effect can win out.
We cannot, however, know in advance if future returns will be concentrated and which companies will be responsible for that concentration. What we do know is that rebalancing and concentration are about trade-offs: rebalancing works because it prevents concentration from building, while a market cap approach works because it allows concentration to develop. The “right” amount of concentration is unknowable in advance, but the more concentrated your approach, the wider the range of outcomes you need to be prepared for.
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Although not its express purpose, Bessembinder’s research is a timely reminder that there is no investing strategy that really constitutes “doing nothing”. Whether it is the precise approach to rebalancing we adopt, when we start investing or the particular index we select there are always choices that we need to make, and these will be consequential.
It is important to be deliberate when doing nothing.
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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).