Which data quality issue is described by duplicate records in surveillance data?

• A. Missing data
• B. Delays in reporting
• C. Misclassification
• D. Duplicate records

Answer: (D)

Duplicate records occur when the same event or person is entered into the surveillance database more than once. In public health surveillance, that means counting the same case multiple times, which inflates incidence and distorts trends, making the data appear more common or recent than it truly is. This happens when data come from multiple sources or when the same submission is entered repeatedly without a deduplication step, often due to inconsistent identifiers or lack of record linkage. The fix is to implement deduplication and robust linking, using unique identifiers and a master dataset to ensure each occurrence is represented once.

Missing data refers to blank fields that prevent complete analysis; delays in reporting mean data arrive later than they should; misclassification happens when a record is labeled with the wrong category.