Which data source combination is described as having strengths of detail and large samples but potential misclassification and missing data?

• A. Questionnaires only
• B. Registries only
• C. Medical records, registries, and questionnaires
• D. Experimental lab data

Answer: (C)

Using multiple data sources can give you both rich detail and broad coverage, but each source brings its own biases. Medical records provide detailed clinical information and longitudinal history, yet coding variations and incomplete entries can lead to misclassification of exposures or outcomes. Registries offer standardized, population-wide data with large sample sizes, but they may miss some variables or have gaps in data quality. Questionnaires can reach very large numbers and capture information not found in records (like lifestyle or self-reported symptoms), but they are vulnerable to recall bias, inaccurate reporting, and missing responses. When you combine medical records, registries, and questionnaires, you get the best of both worlds: detailed data from records and registries plus the broad reach of questionnaires. The trade-off is the introduction of potential misclassification from integrating different data sources and missing data due to nonresponse or incomplete records.