Abstract
This article presents a brief overview of theory as background for a more detailed discussion of midrange theory-its origins, the critical role for midrange theory in the development of nursing practice knowledge, and the criteria for evaluating midrange theory. We then chronicle Cheryl Tatano Beck's program of research on postpartum depression (PPD) and advance the thesis that her theory of PPD, titled Teetering on the Edge, is an exemplar of a substantive midrange nursing theory. We demonstrate Beck's progression from identification of a clinical problem to exploratory-descriptive research, to concept analysis and midrange theory development, and finally to the application and testing of the theory in the clinical setting. Through ongoing refinement and testing of her theory, Beck has increased its generalizability across various practice settings and continually identifies new issues for investigation. Beck's program of research on PPD exemplifies using nursing outcomes to build and test nursing practice knowledge.