Health and illness over time: the trajectory perspective in nursing science.

Background: Understanding change in health and illness over time is central to creating and evaluating interventions for individuals, families, and populations. The term health trajectory is a succinct and useful way to describe change in health status over time.

Objectives: The aims of this article were to define the notion of a health trajectory; comment on the usefulness and current status of health trajectory research for nursing science and practice; and identify and illustrate the key elements of theory, design, and statistical models for health trajectory research.

Approach: Constructs in theory about individual change are summarized, synthesized with characteristics of longitudinal design and statistical models for change, and discussed in light of current and emerging health care priorities and trends in nursing research.

Recommendations: Health trajectory research is person focused and congruent with the person-centered emphasis of nursing practice. The contribution of nursing science to the overall effort to improve health will be enhanced when change over time is explicit in nursing theory, longitudinal designs are used, and contemporary statistical approaches for modeling change in health status are incorporated into research plans.