Mar

11

I think a lot about how attention, like a searchlight, moves around the markets. I like, too, the simple logic that when retail investors are deciding what to buy, they have a huge array of choices, but when deciding what to sell, they are limited to what they own. (Leaving out the idea of looking at thousands of options to try to decide what to short.) Maybe index ETFs simplify this process, but then, before index ETFs we had mutual funds, so maybe not.

All That Glitters: The Effect of Attention and News on the Buying Behavior of Individual and Institutional Investors
Brad M. Barber, Graduate School of Management, University of California, Davis
Terrance Odean, Haas School of Business, University of California, Berkeley
Advance Access publication December 24, 2007

We test and confirm the hypothesis that individual investors are net buyers of attention-grabbing stocks, e.g., stocks in the news, stocks experiencing high abnormal trading volume, and stocks with extreme one-day returns. Attention-driven buying results from the difficulty that investors have searching the thousands of stocks they can potentially buy. Individual investors do not face the same search problem when selling because they tend to sell only stocks they already own. We hypothesize that many investors consider purchasing only stocks that have first caught their attention. Thus, preferences determine choices after attention has determined the choice set.

Asindu Drileba writes:

Laslo Barabasi has a model called preferential attachment. His model can simply be defined as "people usually prefer to bet on a horse that is already winning". I hear night club promoters also do this. To pull in customers, you create artificially fake long lines. These long lines make a night club appear popular, and thus make people interested in going in.

For the S&P index for example, index rebalancing algorithms are at times market cap weighted. That is, stocks with a larger cap, get more money than those with smaller market caps. Which will increase their future allocations, as their market caps grow. Retailers and others seeking "Blue chips" cannot invest in the top 500 stocks. They may focus on the top 20, which further distorts the market caps. Barabasi claims that this is partly why stock market caps have a pareto-like distribution. 20% for stocks may hold 80% of the index value market cap. (I am not saying this so what is exhibited it's just an illustration).

Peter Ringel comments:

I hear night club promoters also do this. To pull in customers, you create artificially fake long lines. These long lines make a night club appear popular, and thus make people interested in going in.

This is one of the many cognitive biases of humans. Any group over 5 attracts attention by by-passers. It even works with cutouts of >5 humans. The research papers above immediately bring my thoughts to manipulation. The searchlight is a daily reality in markets to me. But someone is holding it and is pointing it. Wyckoff style manipulation games on and on. For hundred years. I do disagree a little with the paper about retail trader as the main victim. Institutional smart money today - in one corner of the market - is tomorrows dump money in another corner. They are easily also susceptible to the manipulation games.


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