Selecting Structure Measures for Clinical Quality Measurement

NQMC uses an adaptation of the structure, process, outcome framework for quality measures created by Donabedian. This tutorial explores the structure measure domain. In NQMC, a structure is defined as "a feature of a health care organization or clinician related to the capacity to provide high quality health care." Structure measures include measures of the human and material resources available to the health care system, as well as organizational factors such as staff deployment and protocols. Examples of structure measures include hospital teaching status, ownership, hospital volume, and qualifications of health care providers.

Structure Measures in Perspective

Structure measures are sometimes confused with process measures. Structure measures assess features of delivery organizations, the capabilities of their professionals and staff, and the policy environment in which health care is delivered. That is, they focus on the relatively "fixed" attributes of an organization or its professionals and staff. For example, a measure of whether hospitals have the capability for clinicians to prescribe electronically is a structure measure, while a measure of the number of eligible patients that receive electronic prescriptions is a process measure. The formulation of the measure statement distinguishes between a capability or asset (structure) and the activity that may rely on that structure (process). In addition, structure measures are typically based on the organization or professional as the unit of assessment in the denominator, while a process measure is usually based on patients or care processes in the denominator.
To assess the usefulness of a structure measure, users may wish to seek evidence linking the structural feature with an increased likelihood that a patient receives a process, or that patient outcomes are optimized. The link between structure and process or outcome may be either linear or nonlinear (i.e., more complex). For example, the existence of a hand hygiene staff training course (structure) may be associated with an increase in hand washing before seeing patients (a process) and a reduction in hospital-acquired infections (a health outcome). Other structure measures such as hospital volume or use of electronic health records may capture unmeasured aspects of the care and thus be associated with processes and outcomes in ways that are more complex.

Using Structure Measures

Historically, structure measures have been a mainstay of traditional quality assurance programs that set minimum standards for health care facilities and use these in certification or accreditation programs. For example, the Joint Commission includes numerous structure measures in its accreditation survey, while the Leapfrog Group sets minimum volume standards for hospitals performing specific procedures, such as abdominal aortic aneurysm (AAA) repair or coronary artery bypass grafts (CABG). Some of these same indicators are used as indicators of quality. For example, the AAA and CABG volume indicators are part of the Agency for Healthcare Research and Quality (AHRQ) Inpatient Quality Indicator (IQI) set. Furthermore, the Centers for Medicare & Medicaid Services (CMS) heavily favors structure measures in the assessment of nursing homes.
Structure measures may be relatively straightforward to collect and interpret. However, the link between structure, process, and outcome is affected by multiple factors. A delivery organization may have excellent structural capabilities such as experienced health care providers and well-defined processes of care, but nevertheless fail to deliver care consistently. Some structural measures assess capabilities that cannot be easily modified. For example, low-volume hospitals may have limited capacity to increase patient volume as a way of improving quality. If the link between volume and outcome is mediated by factors other than volume (e.g., post-op nursing protocols), a low-volume hospital could modify these factors and improve outcomes even while remaining a low-volume hospital. These examples argue for caution in over-reliance on structural measures.

Summary

Structure measures assess various features of health care organizations, professionals, or staff. Users may wish to clearly establish the link between a structure and a process or outcome. They are most suitable in accreditation and certification initiatives, but in some instances can serve as proxies for unmeasured processes. For more information on the uses of quality measures, see NQMC's Uses of Quality Measures tutorial.

Questions to Consider When Selecting a Measure of Structure

Is there a strong link between the measured structural feature and the processes and outcomes of care?
Are there intermediate factors that mediate the association between the structural feature and associated processes or outcomes of care?
Is the measured structural characteristic modifiable by the organization, professionals, or other staff?