General concepts in biostatistics and clinical epidemiology: Random error and systematic error

Abstract

Biomedical research, particularly when it involves human beings, is always subjected to sources of error that must be recognized. Systematic error or bias is associated with problems in the methodological design or during the execution phase of a research project. It affects its validity and is qualitatively appraised. On the other hand, random error is related to variations due to chance. It may be quantitatively expressed, but never removed. This review is the first of a methodological series on general concepts in biostatistics and clinical epidemiology developed by the Chair of Scientific Research Meth-odology at the School of Medicine, University of Valparaíso, Chile. In this article, we address the theoretical concepts of error, its evaluation, and control. Finally, we discuss some current controversies in its conceptu-alization that are relevant to undergraduate and graduate students of health sciences.