Omission Bias and Financial Markets

Omission Bias is the tendency to favour the omission of an act over its commission.  It is widely studied in psychology and has been reliably replicated in a variety of scenarios.  In the context of financial markets, this can have adverse effects because there is no practical difference between investing $100 in a stock that declines 10% the next day and failing to buy one that appreciates 10% the next day.

This of course assumes that you actually have $100.  If you don’t have a float of cash available at all times, then you will not be in a position to seize opportunities.  So that would be the first piece of advice.  Maintain a certain percentage of your investable assets in the form of cash —  perhaps 10%.  Alternatively, you could arrange for a line of credit in a similar amount but make sure you do not do too much of this because it is high risk.  Conversely, holding 10% cash acts to reduce risk.

Another adverse effect of Omission Bias is that it impairs your ability to assess performance.  This is of crucial importance.  Many investors do not have clear enough data of what has worked for them and what has not.  It is essential to have a good focus on this for a number of reasons.  

One benefit is that you can only manage your portfolio appropriately if you have been examining its performance precisely.  A second benefit is that you might be able to identify some specific sorts of trade that you are particularly good at.  You can then seek to identify relevantly similar situations and exploit them.  Also — you might have a chance of avoiding disasters from the past occurring again!

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Our ability to look at our failures and learn from them is also impeded by our natural distaste for thinking about the unpleasant — but failures are always more instructive than successes.  One might almost say that any fool can succeed — but only an expert can fail well…

A major practical impediment to any attempts to correct for Omission Bias is due to the sheer scale of the problem.  The number of shares you did not buy yesterday is absolutely huge.  There is no way you can think about all of those.  Nor should you.  The more useful comparison is to think about the shares you could have bought or the ones you almost did buy.  So that tells us that you should be looking at several buy options at a time.  Look at what factors led you to choose the one you did choose.  

Maybe you were looking at three oil companies.  You compared them on price/earnings ratios, dividends and price/book value.  You made a choice.  Did that work out?  (Don’t do this next day.  Wait for a reasonable period.  Otherwise you will just be looking at noise.)

What fundamentally is going on with Omission Bias is a sort of agency effect.  If something bad happens and you could have prevented it but did not, this is seen as morally less culpable than if you did something which caused a bad outcome.  After all, “you didn’t do anything.”  I think this perception might be strengthened by the fact that the law says a lot about what we cannot do but rarely says anything about what you must do.  You are at liberty to walk past a baby drowning in a pond.  You are not at liberty to throw a baby in a pond.

This might be fine morally.  But stock markets are not outlets for moral action.  They are locations where you can profit.  Or not.  Bear in mind the possibilities of Omission Bias affecting your judgements of your own decision-making and your decisions will get better and more profitable.

Learn more in the video below: