Evolving concepts in the measurement of treatment effects.

This is an interesting time in the evolution of clinical research, as the convergence of scientific, social, and technological advances influences the development of new measurement strategies and creates new challenges and opportunities in the evaluation of treatment outcomes. The purpose of this paper is to provide a brief overview of the forces of change influencing clinical research in general and measurement, specifically, discuss current challenges in the evaluation of treatment outcomes in chronic obstructive pulmonary disease and propose several areas for further research. Five key challenges are discussed: accuracy in the selection and measurement of endpoints; appropriate timing and recall; measurement efficiencies using aggregation techniques or item response theory; interpretation, including the debate concerning the minimal important difference; and the need for "real world" studies with real-world measures to understand treatment effectiveness. Each of these areas offers interesting challenges and opportunities for further development and research.