The term tracking error is used to analyze incomplete matching with a benchmark; the SEC discusses this risk for an index fund.[30](#source-cm-index) A quantitative comparison must define the series, frequency and method used to estimate variability. Population and sample standard deviations are not identical, and annualization adds assumptions.
What it does and does not show
A zero average difference does not mean zero variation in every period. Conversely, persistent underperformance can have low variability. Tracking error and tracking difference therefore answer different questions. The series being compared must treat currency, distributions and expenses consistently.
The SEC reminds readers about the expenses of pooled products regardless of the result.[32](#source-cm-fund-types) [Educational deviation series](/guides/index-replication-tracking/) provides a reproducible demonstration, but not a forecast of future accuracy or a complete measure of fund risk.
General concepts; terms of specific contracts and jurisdictions must be checked separately.
Source references and links retained: SEC.[30](#source-cm-index)[32](#source-cm-fund-types), [Educational deviation series](/guides/index-replication-tracking/); series, frequency, population/sample standard deviation, annualization, zero-average distinction, currency, distributions, expenses and fund-risk caveats preserved.
Educational material is not individual investment, legal or tax advice.
