Sometimes called observer error, but “error” is an inappropriate word for this phenomenon. A pervasive problem in all observational studies is that when two or more people examine a patient, an x-ray, an electrocardiogram, a microscopic slide of tissue, blood cells, or other natural phenomena, they do not always agree on what they see and on its significance. The prevalence and magnitude of observer variation can be considerable. When experienced and competent specialists such as radiologists or hematologists examine a series of chest x-rays or blood slides, they may report different findings in 5 to 15 cases per 100. The differences of opinion are not always clinically important but have serious consequences if a life-threatening lesion is overlooked. Observer variation can be devastating for candidates if their answers to examination questions are assessed by a careless, opinionated, or incompetent examiner. Discovery of very high rates of variation in grading of examinations prompted the use of objective tests.
Subjects: Public Health and Epidemiology.