Measurement in Veterans Affairs Health Services Research: veterans as a special population.

Objective: To introduce this supplemental issue on measurement within health services research by using the population of U.S. veterans as an illustrative example of population and system influences on measurement quality.

Principal Findings: Measurement quality may be affected by differences in demographic characteristics, illness burden, psychological health, cultural identity, or health care setting. The U.S. veteran population and the VA health system represent a microcosm in which a broad range of measurement issues can be assessed.

Conclusions: Measurement is the foundation on which health decisions are made. Poor measurement quality can affect both the quality of health care decisions and decisions about health care policy. The accompanying articles in this issue highlight a subset of measurement issues that have applicability to the broad community of health services research. It is our hope that they stimulate a broad discussion of the measurement challenges posed by conducting "state-of-the-art" health services research.