Myopic Loss Aversion

Stop looking at your portfolio.

The Digital Age has made access to stock market data and real-time portfolio values increasingly easy, but it causes investors to lose sight of the big picture as their mental time horizon shortens to match the frequency of feedback rather than that of their planning time horizon.

Loss aversion is a behavioral bias that makes losses hurt about twice as much as a similar sized gain makes us feel good – the result is that investors tend to make poor decisions as a consequence of trying to avoid the pain of a relative or absolute loss.

Myopic loss aversion is the idea that the more we evaluate our portfolios, the higher our chance of seeing a loss and, thus, the more susceptible we are to loss aversion. Additional research shows that investors who get the most frequent feedback also take a less than optimal amount of risk and earn less money.

On the other hand, investors that check their portfolios less frequently are more likely to find gains and less likely to make bad decisions stemming from loss aversion.

Using historical returns on the S&P 500, you have a 47% chance that the market will be down on any given day. However, if you were to wait longer and look at monthly returns, that percentage drops to 38%. If you only look once a year at the past 12 months of returns, the chance you will see a loss drops to 21%.

The table below shows different rolling periods and the percentage of time you would have historically experienced a positive or negative return.

Rolling Performance for the S&P 500 (1926-2016)




54% 46%







6 Months



1 Year



5 Years



10 Years 94%


20 Years 100%


Most investors have a multi-decade time horizon whether they are just beginning to save, in the middle of their careers, or currently in retirement. However, evaluating your portfolio in quarterly or even annual intervals is making an evaluation as if you have a short-term planning horizon.

In addition, outcomes of a probabilistic system such as investing are far too random in the short-term to draw any meaningful conclusions about the success or failure of an investment. Rather than focusing on short-term results, a better course of action would be to evaluate the decision-making process.

A quality decision-making process emphasizes evidence while also protecting us from our faulty mental hardwiring that causes us to misinterpret (or ignore entirely) probabilities, find patterns where none exist, and elicit emotional responses that are detrimental to good investing.

I’m not suggesting that people should only look at their portfolios once every ten years – although I wouldn’t discourage it – but the worst behaved investors I encounter are those that are evaluating the stock market and/or their portfolios over short time periods.

9 thoughts on “Myopic Loss Aversion

  1. Great article! I think as investors we always consider having more information better- having more opinions from others, having instant access to any fundamental information we could want. However, we rarely think how that could affect us as we try to time the market to avoid small losses.

    I think it’s also interesting to consider how access to all of this constant information, advice and opinion affects the market as a whole. For instance, could it be that index funds are overvalued because that’s what all the online advice says?- throw it all in index funds and forget it for 30 years.


    1. Flying Robot

      I’d suggest that it’s (US) equities themselves that show a higher P/E and not the Index funds per se. Low interest rates and relative market stability probably play a role in that too… as a percent of US GDP, prices make a lot of sense, if you control for US Revenue vs Global Revenue. Europe and Emerging Markets currently carry more ‘normal’ valuations.

      Most people have poor investment instincts. A Fidelity study showed the most successful investors at their company were those who forgot about their accounts or whose advisors passed away (!) and were not replaced. In other words, people who bought and sold their investments, on average, lost money at a significant rate. Leaving it along for 30 years seems to be a pretty good strategy.

      I really could never do that, so I have to come up with other ways to keep myself from making unproductive portfolio changes(!)

  2. Asket

    Another great resource to just confirm what you said is by looking at “Investor Return” for each fund provided by Morningstar. They take the money inflow/outflows to calculate a dollar weighted return for the investor base of the entire mutual fund. It is interesting to see that target date funds had a investor return slightly higher than the mutual fund’s time weighted return, while stock funds tend to have investor return lower than the fund’s actual return.

    Also, the higher the standard deviation, the larger the gap between investor return and actual fund return.

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