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GlossaryPublic records, privacy, and data quality

Coverage gap

A coverage gap is an absent agency, period, place, or record category. Learn why missing coverage cannot be treated as zero activity.

A coverage gap is a missing part of the area, period, organizations, or activity a dataset is intended or understood to describe. In a public-safety report, that might mean an absent agency, several unavailable months, or an excluded record category. Missing coverage does not establish that no activity occurred.

The boundary of the available evidence

Coverage describes the reach of the information. A county label, for example, does not by itself establish that every agency operating in the county supplied records. A yearly label does not establish that every month is present.

The FBI's archived 2019 methodology illustrates why this matters: it distinguishes reporting completeness, estimates for missing information, and comparisons based on common agencies and months. Those are historical methods, not a statement of current participation or current estimation procedures. FBI: Crime in the United States 2019 methodology.

Example

Hypothetical: A county dashboard receives records from three municipal departments but has no feed from the sheriff's office. It displays 4,000 incidents for the year.

The number describes the included records from those three departments. It cannot be presented as all county incidents without evidence that the missing source is outside the stated scope or covered through another documented source. Dividing 4,000 by the whole county population would also need justification because the count and population may describe different coverage.

Common confusion

Zero is an observed value under a defined reporting process. A gap is missing evidence. Displaying an absent month as zero turns a reporting limitation into an apparent drop in activity.

A coverage gap also differs from a blank field in an otherwise included record. An incident can be present while its location is missing; that limits mapping even if the total count includes it. Entirely absent incidents raise a different question about the completeness of the source.

Comparing periods with different coverage

Check whether the same sources and periods are included on both sides of a comparison. A higher total after a new agency joins may reflect expanded coverage rather than a rise in activity among the original agencies.

A useful report states the missing portion, its effect on interpretation, and whether an estimate fills it. Estimates should remain distinguishable from directly reported observations. If the size of the missing portion is unknown, a precise percentage of coverage may not be available; describing the known boundary is more honest than implying completeness.

Sources