Which of the following statements describes a limitation of using medical data registries in cohort studies?

• A. They always include complete data for all variables.
• B. They guarantee accurate exposure classification.
• C. They never have missing data.
• D. They may suffer from misclassification and missing data.

Answer: (D)

The main point here is the quality and completeness of data in registries used for cohort studies. Medical data registries are designed for care delivery and billing, not research, so information about exposures and outcomes can be recorded inaccurately (misclassification) and may be incomplete or missing for some patients. This leads to biases in estimated associations and reduces the reliability of findings. For example, a patient’s exposure to a drug might be coded differently over time, or important variables (like smoking status or dose) may not be captured for all records. These issues—misclassification and missing data—are common limitations of registries, whereas the other statements falsely imply that data are always complete, perfectly accurate in exposure classification, or never missing.