Variation is inherent in all phases of the tuberculin testing procedure. The size of the reaction elicited is dependent on many factors besides actual sensitivity (1-4). These factors include, among others, the amount of test material injected, the site of the injection, the depth of the injection, the source and method used in preparing the antigen, and the physiologic state of the patient. Finally, and of prime importance, are the differences in the interpretation of results by different observers. This last variable is the subject of the present study.
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Bearman et al. (1964) studied this question.