In selecting an outcome measure for a study evaluating a nursing intervention, the criterion of sensitivity to change should predominate. Researchers commonly justify their choice of outcome measures for experiments based on such psychometric criteria as high internal consistency reliability and patterns of correlations reflecting convergent and discriminant validity. Although such criteria are appropriate for measures to assess individual differences, they are insufficient when the measures will be used for intervention studies. Researchers may need to develop new measures that are tailored for experimental studies if existing measures are valid mainly for the assessment of individual differences. In this first portion of a two-part article, three of seven factors to consider in selecting an outcome measure for an intervention study are outlined and recommendations for application of principles of reliability and validity in the context of sensitivity to change are given.