This article’s main objective is to demonstrate that data analysis, including quantitative data analysis, is a process of interpretation involving basic hermeneutic principles that philosophers have identified in the interpretive process as applied to other, mainly literary, creations. Such principles include a version of the hermeneutic circle, an insistence on interpretive presuppositions, and a resistance to reducing the discovery of truth to the application of inductive methods. The importance of interpretation becomes especially evident when qualitative and quantitative methods are combined in a single clinical research project and when the data being analyzed are longitudinal. Study objectives will be accomplished by showing that three major hermeneutic principles make practical methodological contributions to an insightful, illustrative mixed methods analysis of a qualitative study of changes in functional disability over time embedded in the Precipitating Events Project—a major longitudinal, quantitative study of functional disability among older persons. Mixed methods, especially as shaped by hermeneutic insights such as the importance of empathetic understanding, are potentially valuable resources for scientific investigations of the experience of aging: a practical aim of this article is to articulate and demonstrate this contention.