Health Services Research (HSR) Methods
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Observational Data
Synonyms: Nonexperimental data
Related Terms: Experimental Data; Selection Bias; Randomization; Missing data

Information not gathered as part of a controlled experiment or from random assignment of study subjects. Observational data are commonly used in social science research, particularly when gathering experimental data would be too costly or unethical. Because the researcher usually has no control over how the data are collected, observational data are more difficult than experimental data to analyze and interpret. Examples of observational data include survey data, administrative records, and standardized test scores. They are also known as nonexperimental data.

Further Reading
Buckley, J, and Shang,Y. ''Estimating Policy and Program Effects with Observational Data: The 'Differences-in-Differences' Estimator.'' Practical Assessment, Research & Evaluation Vol. 8, 2003.

Winship, C. and Morgan, S.L.. ''The Estimation of Causal Effects from Observational Data.'' Annual Review of Sociology Vol. 25, 1999.