Tỷ lệ lệch bao nhiêu là cao? Nắm vững chỉ số BIAS để nhanh chóng đọc tín hiệu mua bán

Many investors often ask during trading: what deviation rate is considered high? In fact, the answer to this question is not absolute, but depends on market conditions, individual stock characteristics, and time cycles. Today, we will delve into the analysis of the deviation rate (BIAS), a practical technical indicator.

The Core Concept of Deviation Rate

What is the deviation rate? Simply put, the deviation rate is an indicator that measures the extent of divergence between the stock price and the moving average line, expressed as a percentage. When the stock price deviates from the moving average, investors’ psychological expectations change — this is exactly what the deviation rate reflects about market sentiment.

The deviation rate is divided into two forms:

• Positive deviation rate: Stock price is above the moving average line, reflecting bullish market sentiment
• Negative deviation rate: Stock price is below the moving average line, indicating bearish market sentiment

Imagine the market like agricultural product trading — during harvest, rice prices soar above historical highs, farmers rush to sell; during reduced production, prices fall below cost, and buyers start large-scale acquisitions. The psychological mechanism in the investment market is exactly the same, with the expectation that “extremes will reverse” driving buy and sell decisions.

How to Calculate the Deviation Rate?

The formula is simple: N-day BIAS = (Closing Price of the Day - N-day Moving Average Price) / N-day Moving Average Price

The moving average price is the average of the security’s price over a certain period, commonly called MA (Moving Average Line). It is important to note that because the moving average line has a lagging nature, the deviation rate calculated based on it also exhibits some lag.

How High Is the Deviation Rate? How to Set Parameters

1. Choose an appropriate moving average cycle

• Short-term trading: 5-day, 6-day, 10-day, 12-day moving averages
• Mid-term trading: 20-day, 60-day moving averages
• Long-term investing: 120-day, 240-day moving averages

2. Determine the deviation rate parameters

Common parameters are 6-day, 12-day, 24-day BIAS. How high the deviation rate is considered high depends on the cycle setting — for example, in a 5-day deviation rate, exceeding 2% to 3% is generally regarded as relatively high, but this is not a rigid rule.

When deciding parameters, consider:

• Liquidity and volatility of the stock (active stocks can use short-cycle BIAS, less active stocks the opposite)
• Current market sentiment (bull and bear markets show significant differences in deviation rate performance)
• Your trading cycle and risk tolerance

3. Set buy and sell thresholds

Before using BIAS, you need to set positive parameters (overbought line) and negative parameters (oversold line). In highly volatile markets, these thresholds will be frequently broken, so they should be flexibly adjusted based on historical data and market environment.

Using Deviation Rate to Precisely Find Buy and Sell Points

Overbought and oversold judgments

• BIAS above the positive parameter (how high is the deviation rate? exceeding the threshold indicates overbought) → downward pressure increases → consider selling
• BIAS below the negative parameter (below the negative parameter indicates oversold) → upward momentum appears → consider buying

Combine with multiple moving averages for deep analysis

Relying on a single BIAS can lead to misjudgments. Combining the deviation rates of the 5-day and 20-day moving averages allows simultaneous observation of short-term and medium-term trends, improving judgment accuracy.

The importance of divergence phenomena

Divergence is a key signal for judging turning points:

• Price hits a new high, but the deviation rate does not reach a new high → possible top signal, beware of downside risk
• Price hits a new low, but the deviation rate does not reach a new low → possible bottom signal, increasing rebound opportunities

Limitations and Usage Restrictions of the Deviation Rate

1. Limited utility for consolidating stocks

When stocks fluctuate slightly over a long period or experience slow rises and falls, the guidance role of the deviation rate diminishes significantly, and false signals may occur.

2. Lagging risk

Since the deviation rate is based on the moving average line, it inherently has a lagging characteristic. It is not recommended to rely solely on it for selling decisions, but it can serve as a reference for buying.

3. Market capitalization differences affect judgment

Large-cap stocks are more stable, and the deviation rate’s accuracy is higher; small-cap stocks are more volatile, and relying solely on the deviation rate reduces accuracy.

Practical Suggestions to Improve BIAS Effectiveness

Combine with other technical indicators

Using BIAS together with stochastic indicator KD and Bollinger Bands BOLL yields better results. BIAS combined with KD is suitable for rebound trading timing, while BIAS combined with BOLL is more suitable for buying during oversold rebounds.

The art of parameter selection

Too short a cycle can be overly sensitive and generate noise; too long a cycle reacts sluggishly. Find a balance between sensitivity and stability.

Flexible application based on stocks

Stable stocks with good performance rebound quickly when falling because investors fear missing opportunities; weak stocks with poor performance may not rebound for a long time, so signals from the deviation rate should not be blindly followed.

How high the deviation rate is considered high has no absolute answer. Only by combining market environment, stock fundamentals, multiple technical indicators, and your own trading style can you truly master the BIAS indicator and improve your trading success rate.