🎯Kelly Criterion and Risk Management: How to Determine Position Size
Kelly Criterion and Risk Management: How to Determine Position Size
Introduction to the Kelly Criterion
The Kelly Criterion is a mathematical formula used to determine the ideal size of a bet (position) based on the probability of success and potential return. This concept has become popular among investors and traders as it helps maximize long-term capital growth while minimizing risk.
The Kelly Criterion Formula
The formula for calculating the ideal position size is as follows:
**f* = (bp - q) / b
- f*: proportion of capital to be invested in the position
- b: potential return (how many units you gain for each unit invested)
- p: probability of success
- q: probability of failure (q = 1 - p)
Example of Using the Formula
Imagine you are investing in AAPL stock, estimating a 60% chance of price increase (p = 0.6). If the current stock price is $150 and you believe the stock will rise to $180, your potential return (b) is 0.2, since with a $150 investment, you gain $30 in profit.
With this data:
- p = 0.6
- b = (180-150)/150 = 0.2
- q = 1 - p = 0.4
You can substitute these values into the formula:
f = (0.2 0.6 - 0.4) / 0.2 = (0.12 - 0.4) / 0.2 = -0.14 / 0.2 = -0.7
In this case, a negative output means you should not invest in that position.
Fractional Kelly
Fractional Kelly means investing only a portion of the size recommended by the Kelly Criterion, reducing risk. For example, 1/4 Kelly. If your Kelly calculation recommends investing 10% of your capital, you would only invest 2.5% physically.
This strategy is ideal for conservative investors who do not want to take on excessive losses.
Practical Example Using QMA Alpha Signal Engine
Within the QMA platform, we have an Alpha Signal Engine feature that generates signals based on data analysis, allowing you to assess the probability of success of your investment. This tool also provides coded confidence scores that help you evaluate how strong a specific investment signal is.
Example of Using Alpha Signal Engine:
Using the Kelly criterion:
f = (0.2 0.75 - 0.25) / 0.2 = (0.15 - 0.25) / 0.2 = -0.10 / 0.2 = -0.5
This output suggests you have no reasons to invest in AAPL unless you intend to apply fractional Kelly.
Maximum Position Size
It is advised to maintain a maximum single position size at around 5% of your capital. This limit helps to diversify your portfolio risk and prevents excessive losses if a trade does not go as expected. Utilizing the qma-picks feature in QMA allows you to track and optimize your investment portfolio to ensure adherence to this policy.
Where to find this in QMA
- Alpha Signal Engine
- Stock Screener for Analysis
- QMA Picks for Tracking Recommendations
- 5-pillar score for Evaluating Stock Quality**
Conclusion
The Kelly Criterion is a powerful tool for investors looking to optimize their investment strategies. With proper calculations and possible use of fractional Kelly, you can manage your risks and effectively allocate your capital. Always remember that diversification and adhering to maximum position sizes are key to maintaining a healthy investment portfolio.
Disclaimer
There is a risk of capital loss with any investment. You should consult with a qualified financial advisor before making any investment decisions.
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Create a free accountContent created by AI in collaboration with Jaroslav Vojtášek. Not investment advice. The author may hold the stocks mentioned. Investing involves risk of loss.
Operator: Jaroslav Vojtášek, Company ID (IČO) 48783447.