Bias Ratio

Article byAswathi Jayachandran
Edited byRashmi Kulkarni
Reviewed byDheeraj Vaidya, CFA, FRM

What Is Bias Ratio?

The bias ratio is a numerical measure to evaluate the likelihood of the fund’s returns distribution being manipulated. When analyzing the returns of equity indices, a relatively unbiased returns distribution will typically have a bias ratio close to 1. The purpose of this ratio is to indicate the possibility of price manipulation in fund or investment prices, detect fraud (if any), and verify the authenticity of investment management.

Bias Ratio

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Hedge funds are crucial in investment markets but undergo increased scrutiny due to high-profile frauds and market manipulation. When used alongside other metrics, the bias ratio can provide reliable evidence about the authenticity of a hedge fund. It compares the actual asset return distribution to unbiased returns, offering a reliable and early indication of fraudulent activity.

Key Takeaways

  • The bias ratio is a numerical measure used to evaluate the chances of manipulation in a fund’s returns distribution.
  • The ratio uses fund returns as input data and compares them with unbiased returns. These results directly relate to return smoothing; a higher ratio suggests that the normally distributed returns will be close to 1.
  • Adil Abdulali, a risk manager at Protégé Partners, developed the bias ratio indicator. 
  • It is a metric that shows promising results in identifying fraudulent activities such as insider trading. These ratios effectively help uncover return manipulation when combined with other metrics.

Bias Ratio Explained

The bias ratio is a mathematical tool that helps signal or detect funds that commit fraud. The ratio uses fund returns as input data and compares them with unbiased returns. These results directly relate to return smoothing, particularly hedge fund returns smoothing.

Higher ratio suggests that returns following a normal distribution will be close to 1. Funds valued using market prices (funds that invest in liquid securities) will also have a bias ratio close to 1. This is because smoothing the liquid securities returns is challenging. Illiquidity can lead to high bias ratios in securities that are hard to price, even without fraud.

The metric can almost always accurately identify fraudulent activities such as insider trading. It helps uncover return manipulation when combined with other metrics. Detecting investment fraud early can insulate investors from potential losses of a considerable magnitude. Adil Abdulali, a risk manager at Protégé Partners, developed the bias ratio, which can also be called the bias ratio indicator. He developed it based on his experience in managing a hedge fund, investing with various managers, and trading on the sell side.

Although damages due to fraud in financial markets are common, hedge fund frauds have brought the industry under considerable scrutiny. However, uncovering fraud in hedge funds can be difficult as they do not have the same transparency, disclosure policies, or record maintenance as mutual funds. It must be noted that detecting fraud in mutual funds may also be challenging at times.

Like hedge funds, mutual funds may invest in illiquid securities, which can be hard to price, making a fund’s Net Asset Value (NAV) subjective. This allows fund managers to manipulate the NAV, which may lead to negative or positive return figures or projections being presented or promised to investors. Typically, manipulation shows a reduction in fund volatility, which improves risk-adjusted performance, making them attractive to investors.

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How To Calculate?

The bias ratio technical indicator can be represented mathematically by the following formula.

Bias Ratio=  Count(ri):riε[0,+1.0σ]/ 1+Count(ri):riε[−1.0σ,0]


  • i represent the time index
  • Ri represents the return for a month i


Listed below are a few examples to explain the concept in greater detail.

Example #1

Dan, an investor, wants to invest in BC Ltd. (a water purifier manufacturing company) and decides to use the bias ratio to decide whether to invest in the company. He does it simply by subtracting S&P 500 returns from the average return of water manufacturing companies for the past few years. In the next step, the result is divided by the stock’s standard deviation returns.

Let us say the bias ratio of the industry is 1.5%. This means the stock of the water purifier manufacturing company has been outperforming the S&P 500 by 1.5% in the past few years. The high standard deviation of more than 1% shows the company’s stocks have been volatile. Using this information, Dan can now chart his investment based on his financial goals and decide if investing in this company will prove beneficial.

Example #2

Hedge funds played a role in the 2008 Global Financial Crisis and may have exacerbated the Asian Financial Crisis. However, the collapse of Long-Term Capital Management (LTCM) in 1998 was conclusive proof that hedge funds can have detrimental effects on the market. Many hedge fund managers sought new, prospective investment instruments after the Dot Com bubble.

Many saw opportunities in the market for subprime derivatives and used them. A study titled “Detecting Investment Fraud Using the Bias Ratio” found that the bias ratio can detect anomalies in portfolio returns. It is considered a common indicator of deliberate change, more commonly referred to as fraudulent manipulation.

The study concludes with an example of Madoff Securities, where fund managers meddled heavily to manipulate return trends and projections. The impact of the fraud could have been lowered if the bias ratio had been employed as a metric to detect and highlight fraud. Instead, the Sharpe Ratio was applied. Only the bias ratio could have allowed for deeper investigation and early fraud detection. This shows how effective the bias ratio is at spotting fraud.

The bias ratio was also helpful in spotting anomalous or abnormal returns, as proven by the portfolio returns analysis conducted later by funds convicted of insider trading, including SAC Capital and The Galleon Group.

Frequently Asked Questions (FAQs)

1. What is the bias ratio technical indicator?

The bias ratio is a quantitative indicator that can identify valuation bias or intentional price manipulation of portfolio assets by a hedge fund manager. It also extends to mutual funds or similar investment vehicles that do not need to be transparent about investors’ actuarial holdings.

2. What other financial ratios should an investor consider alongside the bias ratio?

Other ratios that can help investors evaluate the performance of stocks are the Sharpe ratio, debt-to-equity ratio, price-to-earnings ratio, return on equity ratio, current ratio, etc. Apart from these, a comprehensive ratio analysis can also help review financial statements and verify if investment decisions are correct.

3. Where can I find historical data for the bias ratio?

Historical financial market data can be obtained from a variety of sources. Online financial news sources, brokerage houses, and financial data providers such as FactSet are good options. These suppliers provide a wide range of financial information that can be used to assess the S&P 500 index’s performance over time.

This article has been a guide to What Is Bias Ratio. Here, we explain the concept in detail with its examples and how to calculate it. You may also find some useful articles here –

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