Clinical, medical, and health psychologists use difference scores obtained from pretest–posttest designs employing the same test to assess intraindividual change possibly caused by an intervention addressing, for example, anxiety, depression, eating disorder, or addiction. Reliability of difference scores is important for interpreting observed change. This article compares the well-documented traditional method and the unfamiliar, rarely used item-level method for estimating difference-score reliability. We simulated data under various conditions that are typical of change assessment in pretest–posttest designs. The item-level method had smaller bias and greater precision than the traditional method and may be recommended for practical use.

临床，医学和健康心理学家使用从前测后测设计中获得的差异评分（采用相同测试）来评估可能由干预措施引起的个体内变化，例如，焦虑，抑郁，进食障碍或成瘾。差异评分的可靠性对于解释观察到的变化很重要。本文比较了有据可查的传统方法和不熟悉的，很少使用的项目级方法来估计差异评分的可靠性。我们在各种条件下对数据进行了模拟，这些条件在前测-后测设计中通常是变更评估的结果。与传统方法相比，项级方法具有较小的偏差和更高的精度，可以建议实际使用。