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cover of episode Money Talks: Can Math Really Crack the Stock Market? (Encore)

Money Talks: Can Math Really Crack the Stock Market? (Encore)

2024/12/24
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Felix Salmon
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Mary Childs
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Felix Salmon: 股票价格并非客观真理,其背后存在模糊性,尤其是在涉及股票总量时。 Mary Childs: Fama-French模型的数据存在被操纵的嫌疑,其提供的资产价格数据集存在数据变动的问题,且缺乏清晰的说明或披露。在实践者和学术界(特别是商业法和实证金融领域)之间存在文化差异,对Fama-French数据集变动问题的重视程度不同。Fama-French免费公开分享的数据集扩大了其影响力,但也使其数据变动问题更加突出。商业法领域需要精确的数据,而实证资产定价领域则更接受数据的不确定性。 Eugene Fama和Kenneth French:构建数据集时会做出许多微小的任意选择,这些选择会影响最终结果;数据提供商自身的数据变化也会影响最终结果;数据变化似乎是有规律地提高了价值型股票的回报率。回应质疑时,他们强调了模型的不确定性和风险性,并暗示批评者对实证经济学的理解不足。 Mary Childs: Dimensional Fund Advisors 基金管理规模巨大,其投资策略依赖于 Fama-French 模型,并声称其策略能够跑赢大盘。然而,其策略的有效性依赖于价值型股票跑赢大盘的假设,而该假设的可靠性正受到质疑。

Deep Dive

Key Insights

Why did the Fama-French data set become so important in the business law community?

The Fama-French data set became crucial in the business law community because it is used to calculate damages in securities litigation. When a company makes a mistake and the stock price drops, the Fama-French factors provide an alternate universe version of how the stock would have performed, which helps in estimating the damages.

Why did the numbers in the Fama-French data set change over time?

The numbers in the Fama-French data set changed over time due to various factors, including underlying data changes from data providers, arbitrary choices in constructing the data set, and methodological adjustments. These changes, while small individually, can compound over time and significantly affect long-term returns.

Why did the changes in the Fama-French data set raise suspicion?

The changes in the Fama-French data set raised suspicion because they consistently improved the returns of the value factor, which Fama and French are famous for promoting as outperforming the market. This consistent improvement seemed fishy and led to questions about the reliability and transparency of the data.

How does the concept of p-hacking relate to the Fama-French model?

P-hacking relates to the Fama-French model because it involves finding statistically significant results in data by making multiple comparisons or adjustments. The garden of forking paths concept suggests that researchers can unintentionally find and promote factors that appear significant but are actually just noise. This raises questions about the robustness of the value factor identified by Fama and French.

What is the significance of Dimensional Fund Advisors in this story?

Dimensional Fund Advisors is significant because it manages $677 billion in assets and is founded by a former student of Eugene Fama. Dimensional charges high fees and bases its investment strategy on the Fama-French factors, particularly the value factor. The firm's success and the reliability of its data set are central to the controversy.

Why did Fama and French's response to the noisy factors paper seem dismissive?

Fama and French's response to the noisy factors paper seemed dismissive because they wrote an 18-page paper explaining their methodology without directly acknowledging or naming the noisy factors paper. They ended with a warning about the unreliability of asset pricing models, suggesting a lack of concern and a middle-finger attitude towards the criticism.

What is the broader implication of the changes in the Fama-French data set?

The broader implication of the changes in the Fama-French data set is that it raises questions about the reliability of financial models and the potential for bias or noise in empirical finance. It highlights the need for transparency and rigorous methods in constructing and maintaining financial data sets, especially those used in high-stakes decisions like litigation and investment.

Chapters
This chapter explores the Fama-French model, a tool used for predicting the stock market. The model's numbers keep changing, raising questions about the nature of investing and market reality. The discussion begins with the author's experience at a business law conference.
  • Fama-French model for stock market prediction
  • Numbers in Fama-French model keep shifting
  • Cultural schism between practitioners and academics regarding the model

Shownotes Transcript

The “Fama–French model” is a Nobel laureate-designed tool for predicting the stock market. It guides hundreds of billions in investments. The problem? Its numbers keep shifting. For this Money Talks, Felix Salmon) chats with Planet Money host Mary Childs about her deep dive for Bloomberg) into finance mathematics. They question the nature of investing, markets, and reality itself. Mary is also the author of The Bond King).

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Podcast production by Jared Downing and Cheyna Roth.

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