Errors in the necessary information (e.g., in exposure measurement) that are not related to the state of disease. This is the case if equal proportions of subjects in the groups, which are compared, are classified incorrectly with respect to exposure or disease. Also known as nondifferential misclassification. This type of misclassification dilutes the true difference and therefore always changes the observed effect toward the null hypothesis (i.e., no relationship between exposure and disease).