Calculate the variation in active returns
For n matched observations, let a[t] = R_strategy[t] - R_benchmark[t] and mean_a = sum(a[t]) / n. This page uses sample tracking error: TE_period = sqrt(sum((a[t] - mean_a)^2) / (n - 1)), with n at least 2. Enter returns consistently as decimals. Multiplying the final result by 100 displays percentage points of return volatility.
- An uncentered root mean square, sqrt(sum(a[t]^2) / n), also includes the average gap. It is not the centered sample standard deviation used here.
- Some reports use a population denominator n. That choice gives a different result, especially in a short sample; record the convention when reconciling reports.
| Statistic | Calculation | Interpretation |
|---|---|---|
| Mean active return | Average of periodic return differences | The average direction and size of the gap |
| Tracking error | Standard deviation of periodic return differences | The variability around that average gap |
| Cumulative tracking difference | Compounded strategy return minus compounded benchmark return over the same dates | The realized endpoint performance gap |
| Information ratio | Mean active return divided by tracking error, using compatible units | Average active return per unit of active risk |