Short Answer: Lucky Numbers Do Not Help Profits, and There Is Evidence They Hurt
On Taiwan's futures exchange, retail investors placed far more orders at prices ending in 8 than at prices ending in 4, and the group showing that behavior lost more than the rest. In another direction, stocks chosen for auspicious numbers at listing had lower subsequent abnormal returns. These are two independent pieces of evidence pointing to one conclusion: choosing prices and tickers by lucky numbers brings no advantage, and comes with worse outcomes.
Why Do Investors Who Favor the Number 8 Lose More?
The answer lies in the fact that the belief changes not only how prices are chosen, but also when orders are placed and how long positions are held. Research by Utpal Bhattacharya and coauthors, published in 2018 in Management Science, found that retail investors who favor the number 8 not only placed more orders at prices ending in 8, but also tended to pick worse timing and hold positions too long.
Three mechanisms are separated in this research:
- Choosing prices by lucky numbers: prices ending in 8 were preferred over those ending in 4, even though the two levels are nearly economically equivalent.
- Poor timing: investors who favor the number 8 tended to enter at less favorable moments.
- Holding too long: positions were kept longer than reasonable, raising opportunity cost and risk.
These three factors combine to create the profit gap. The notable point is that this result does not say the belief itself causes losses, but that the belief changes behavior, and behavior changes outcomes. This is the correct way to understand the self-fulfilling effect: the effect is real, but it arises from behavior, not from the number being sacred.
Do Auspicious Tickers at Listing Have Lower Returns?
Yes. Research by David Hirshleifer and coauthors, published in 2018 in Management Science, found that stocks chosen for auspicious numbers at listing had lower subsequent abnormal returns. The data for this research came from mainland China, and it was published in a US academic journal. The scope of that data needs to be stated clearly: this result does not automatically carry over to the Vietnamese market or to Vietnamese people, because no corresponding research on Vietnamese data exists.
The mechanism here differs from the order-placing case. When a company chooses a listing ticker by auspicious numbers, investors may be drawn to that ticker for the pleasant feeling, and the price is pushed above fair value. When the price corrects to fair value, subsequent returns are lower. This is a form of mispricing due to psychological factors, not business quality.
Price Clustering at Last Digits: A Common Phenomenon Across Markets
Price clustering at certain last digits is not unique to one exchange. Research by Philip Brown and coauthors, published in 2002 in Pacific-Basin Finance Journal, found that price clustering by last digit appears in Asia-Pacific stock markets. This is evidence that cultural factors influence how prices are set, not only purely economic factors.
The table below summarizes the main studies used in this article:
| Study | Data scope | Main finding | Evidence level |
|---|---|---|---|
| Bhattacharya et al. (2018), Management Science | Taiwan futures exchange | Retail investors who favor 8 place more orders at prices ending in 8 than 4, pick worse timing, hold longer, lose more | A |
| Hirshleifer et al. (2018), Management Science | Mainland China stock listings | Auspicious tickers have lower abnormal returns after IPO | A |
| Brown et al. (2002), Pacific-Basin Finance Journal | Asia-Pacific stock markets | Price clustering by last digit | A |
| Kolb and Rodriguez (1987), The Journal of Finance | US market, Friday the 13th | Reported lower returns on Friday the 13th | B |
| Dyl and Maberly (1988), The Journal of Finance | US market, longer data series | Friday the 13th effect does not exist when the sample is extended | A |
Friday the 13th: An Anomaly That Disappears with More Data
The Friday the 13th story is the clearest example of why an effect must be verified repeatedly before it is believed. In 1987, Robert W. Kolb and Ricardo J. Rodriguez published in The Journal of Finance a report showing that US stock market returns were lower on Friday the 13th. This result once drew attention as a market anomaly.
But only a year later, in 1988, Edward A. Dyl and Edwin D. Maberly published in the same journal a response showing that with a longer data series, the Friday the 13th effect does not exist. In other words, the initial result was a false positive: it appeared in a small sample, then vanished when the sample was extended. This is why the evidence level of the 1987 report is ranked as level B in this article: that result has not been replicated, and has been refuted with better data.
The lesson from this case applies to any claim about lucky numbers and returns: a positive result in a small sample is not enough to conclude, and must be verified on independent data before being used for decisions.
Belief Changes Behavior, Behavior Changes Outcomes: Understanding the Self-Fulfilling Effect Correctly
When an effect is real but arises from belief, its nature must be described correctly. Belief in lucky numbers changes how orders are placed, and how orders are placed changes trading outcomes. The effect is real at the behavioral level, but not because the number has supernatural power. In other words, it should not be called the system predicting correctly, nor should it be denied that the effect exists.
This understanding helps distinguish two different questions:
- First question: does the number 8 bring luck? This is a question about belief, and science has no evidence for a supernatural causal mechanism.
- Second question: do people who believe in the number 8 behave differently, and does that behavior affect outcomes? This is a question about behavior, and the answer is yes.
These two questions are often merged in debates, leading to misunderstanding on both sides.
Where Evidence Is Missing: No Vietnamese Exchange Data Yet
An important point to state clearly: the studies cited in this article do not use Vietnamese stock market data. The order-placing research used Taiwan futures exchange data. The listing research used mainland China data. The price clustering research used data from several Asia-Pacific markets. The Friday the 13th case used US market data.
Therefore, the degree of influence of lucky-number choices on Vietnamese investors' returns cannot be asserted without research on Vietnamese data. What can be said is that the general trend in the markets studied points in one direction: choosing by lucky numbers creates no advantage. This is an inference from similar markets, not a direct conclusion for the Vietnamese market.
How Should This Result Be Read Correctly?
The research results do not say that people who believe in lucky numbers are uninformed, nor do they deny the role of culture in economic life. Culture influences how people set prices, choose tickers, and choose timing, and that is recorded in the data. What the studies show is that when cultural factors override economic factors in investment decisions, outcomes tend to be worse.
For readers interested in investing, the message here is about method: verify with data, do not rely on feelings about numbers. For readers interested in culture and psychology, the message is about mechanism: belief changes behavior, behavior changes outcomes, and that is why the effect can be observed even when no supernatural mechanism exists.
