Definition / Meaning of Tracking error
Tracking error is a measure of how closely a mutual fund or exchange-traded fund (ETF) follows its benchmark index. In simple terms, it tells you the difference between the returns of a fund and the returns of the index it is trying to copy or beat. A small tracking error means the fund closely follows the index, while a large tracking error means the fund’s performance is drifting away from the index.
Think of tracking error as a scorecard for how well a fund manager is sticking to their game plan. For passive investing funds, like index funds, the goal is to have a very low tracking error. These funds aim to replicate the index as perfectly as possible. For active funds, a higher tracking error is expected because the manager is trying to pick winning stocks that differ from the index, hoping to beat the market. However, if an active fund has a high tracking error but also poor returns, it is a red flag.
How Tracking Error is Calculated
Tracking error is calculated using the standard deviation of the difference between the fund’s returns and the benchmark’s returns over a specific period. The formula is often expressed as:
Tracking Error = √[ ∑(Rfund – Rbenchmark)2 / (N – 1) ]
Where:
- Rfund is the return of the fund in a given period
- Rbenchmark is the return of the benchmark index in the same period
- N is the number of periods (often months or days)
This calculation gives you a single number, usually expressed as a percentage. For example, a tracking error of 0.50% means that the fund’s returns have typically deviated from the index by about half a percentage point each month. The lower the number, the closer the fit.
Why Tracking Error Matters
Tracking error is crucial for several reasons. First, it helps you understand the true cost of investing in a fund. Even if a fund has a low expense ratio, a high tracking error can eat into your returns. For example, if an index fund charges 0.10% in fees but has a tracking error of 1%, you are effectively losing more than the stated fee due to poor replication.
Second, tracking error helps you set realistic expectations. If you buy an ETF that tracks the S&P 500, you expect returns similar to the index. A high tracking error means your actual returns could be noticeably different, for better or worse. This is especially important for short-term investors who may be surprised by unexpected divergence.
Third, for financial advisors and institutional investors, tracking error is a key component of risk management. It is used to evaluate whether a fund manager is delivering on their promise. If a manager claims to be a passive indexer but has a rising tracking error, it could signal style drift or poor management.
Factors That Influence Tracking Error
Several factors can cause a fund to have a higher tracking error. These include:
- Management fees and expenses: Even small fees create a drag on returns, causing the fund to lag the index slightly. This is the most common source of tracking error for passive funds.
- Cash drag: Mutual funds often hold a small amount of cash to handle redemptions. Since cash earns less than stocks, this can cause the fund to trail the index.
- Sampling: Some index funds do not buy every single stock in the index (especially if the index has thousands of holdings). Instead, they buy a representative sample. This sampling can lead to small differences in performance.
- Replication method: ETFs using physical replication (holding the actual securities) tend to have lower tracking error than those using synthetic replication (using derivatives).
- Trading costs: When the index rebalances, the fund must buy and sell stocks, incurring commissions and bid-ask spreads, which add to tracking error.
- Corporate actions: Events like stock splits, dividends, and mergers must be handled by the fund. Any delay or inefficiency can create a slight deviation.
Tracking Error vs. Alpha
Tracking error is often confused with alpha, but they are different. Alpha measures the excess return of a fund compared to its benchmark, adjusted for risk. Tracking error measures the volatility of that excess return. In other words, alpha tells you how much a fund beat the index, while tracking error tells you how consistently it follows the index. A fund with high alpha and high tracking error is a volatile outperformer, while a fund with low alpha and low tracking error is a steady index hugger.
Practical Example
Suppose you are comparing two ETFs that both track the S&P 500. Fund A has an annual tracking error of 0.10%, while Fund B has a tracking error of 0.80%. Over a year, Fund A will likely deliver returns within 0.10% of the S&P 500, while Fund B could be off by 0.80% or more. Unless Fund B has a significantly lower expense ratio, Fund A is clearly the better choice for a passive investor. If you are an active investor, a tracking error of 2% or more might be acceptable if the manager is consistently beating the index by 3%.
In summary, tracking error is a simple but powerful tool for evaluating how well a fund is performing relative to its stated benchmark. Whether you are a buy-and-hold indexer or a risk-seeking active trader, understanding tracking error helps you make smarter investment decisions.