Doctor of Philosophy
Thomas T. H. Wan
This research developed and tested a conceptual model to explain why higher volumes of certain surgical procedures lead to better patient outcomes. The model incorporated hospital structural characteristics and process of care indicators to explain the volume-outcome relationship. The volume-outcome relationship was further examined longitudinally to determine stability over time and to substantiate the causality implied by the conceptual model.
A sample (n=1752) of acute-care, general hospitals was selected from hospitals that performed, in 1990, at least one surgical procedure on Medicare patients of the following: reduction of hip fracture, cholecystectomy, hip replacement, carotid endarterectomy, and pacemaker insertion. For the longitudinal analysis, the sample size was reduced to 1582 hospitals that performed all five surgical procedures in 1988 and in 1990. The conceptual model was specified as a structural equation model, and was analyzed using LISREL 7. The cross-sectional analysis examined interrelationships among volume, resource availability, average length of stay, structure, process, and outcome. Panel data were used to examine the stability of volume and outcome from 1988 to 1990.
The hypothesized volume-outcome relationship existed for hip fracture and cholecystectomy, and the effects of structure and process on outcome were significant for hip fracture and hip replacement. No volume effects were detected for hip replacement, carotid endarterectomy, and pacemaker insertion. In all cases, volume, average length of stay, and resource availability had significant influence on the hospital's structure and process of care. Panel data were relatively stable for volume, but unstable for outcome.
The volume-outcome relationship is procedure-specific. For hip fracture and cholecystectomy, the direct effect of volume on outcome is small after taking into account structure and process. The indirect effect of volume leads to inefficient care processes and attenuates the beneficial, direct effects of high volume.
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