Cognitive Biases And How They Affect Stock Markets

There are an extraordinarily large number of cognitive biases which change the way we think — it is important to know about these in stock markets both in order to look for them in one’s own thinking and expect them in that of other market participants

A Cognitive Bias is an element in our psychology which makes decisions for us.  In fact, given there are so many of them, you might even say that our psychology is just Cognitive Biases.  I discuss about 20 of them and give market context in my new book:

One example which I discussed in a previous post is Hindsight Bias.  This makes us think that everything which has happened was inevitable.  This in turn makes us very bad at knowing what level of probability we assigned to past events.   We seem to remember that we said that a prior event was going to occur with 90% probability when in fact, we gave it a probability of 30% before that event occurred.  This will obviously have unhelpful effects in the context of markets.  It will make us greatly overestimate our chances of knowing what is going to happen next, which may make us trade with over-confidence.  There is nothing quite like over-confidence to kill market performance.

As I said, the book covers around 20 biases and their effects in markets in much more detail than I can give above.  The thing is though, that there are way more biases than that.  In fact, from the chart below, which is due to Bence Nanay, you can see just how many there are.

Every one of these biases will affect your market thinking and that of everyone else involved.  So it looks like we all have some work to do!

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Author: Tim Short

I went to Imperial College in 1988 for a BSc(hons) in Physics. I then went back to my hometown, Bristol, for a PhD in Particle Physics. This was written in 1992 on the ZEUS experiment which was located at the HERA accelerator in Hamburg ( I spent the next four years as a post-doc in Hamburg. I learned German and developed a fondness for the language and people. I spent a couple of years doing technical sales for a US computer company in Ireland. In 1997, I returned to London to become an investment banker, joining the legendary Principal Finance Group at Nomura. After a spell at Paribas, I moved to Credit Suisse First Boston. I specialized in securitization, leading over €9bn of transactions. My interest in philosophy began in 2006, when I read David Chalmers's "The Conscious Mind." My reaction, apart from fascination, was "he has to be wrong, but I can't see why"! I then became an undergraduate in Philosophy at UCL in 2007. In 2010, I was admitted to graduate school, also at UCL. I wrote my Master's on the topic of "Nietzsche on Memory" ( Also during this time, I published a popular article on Sherlock Holmes ( I then began work on the Simulation Theory account of Theory of Mind. This led to my second PhD on philosophical aspects of that topic; this was awarded by UCL in March 2016 ( -- currently embargoed for copyright reasons). The psychological version of this work formed my book "Simulation Theory". My second book, "The Psychology Of Successful Trading: Behavioural Strategies For Profitability" is in production at Taylor and Francis and will be published in December 2017. It will discuss how cognitive biases affect investment decisions and how knowing this can make us better traders by understanding ourselves and other market participants more fully. I am currently drafting my third book, wherein I will return to more purely academic philosophical psychology, on "Theory of Mind in Abnormal Psychology." Education: I have five degrees, two in physics and three in philosophy. Areas of Research / Professional Expertise: Particle physics, Monte Carlo simulation, Nietzsche (especially psychological topics), phenomenology, Theory of Mind, Simulation Theory Personal Interests: I am a bit of an opera fanatic and I often attend wine tastings. I follow current affairs, especially in their economic aspect. I started as a beginner at the London Piano Institute in August 2015 and passed Grade Two in November 2017!

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