Hamilton B H, Ho V
John M. Olin School of Business, Washington University, St. Louis, MO 63130, USA.
Med Care. 1998 Jun;36(6):892-903. doi: 10.1097/00005650-199806000-00012.
Most tests of the practice-makes-perfect hypothesis have used cross-sectional data, which reveal that patients receiving surgery in high-volume hospitals tend to experience better postsurgery outcomes. This study uses longitudinal data to explicitly examine whether any given hospital's patient outcomes change as its surgery volume varies with time.
Longitudinal data from all hospitals conducting hip fracture surgery in Quebec between 1990 and 1993 were used to examine the relationship between surgery volume and outcomes. The longitudinal data allowed volume to be measured using the actual number of surgeries performed by the admitting hospital in the 12 months before a patient's surgery. Determinants of postsurgery length of stay were assessed using ordinary least squares regression, and the explanators of inpatient mortality were identified using logistic regression. The regressions included fixed effects (hospital-specific dummy variables) to control for systematic differences in outcomes across hospitals that persist with time. Therefore, the coefficient on hip fracture surgery volume in the regression models captured differences in outcomes that were attributable to changes in surgery volume within hospitals with time.
The fixed effects were significant explanators of both postsurgery length of stay and inpatient mortality, indicating that there were significant differences in outcomes across hospitals that persisted with time. In regressions that excluded the fixed effects, the coefficient on surgery volume was significant. In contrast, the coefficient on surgery volume was insignificant when the fixed effects were included.
Longitudinal data revealed that after controlling for differences in hospital outcomes that were fixed with time, hospitals performing more surgeries in one period than in another experienced no significant improvement in outcomes. These results do not support the "practice makes perfect" hypothesis. The volume-outcome relationship for hip fracture patients thus appears to reflect fixed differences in quality between high-volume and low-volume hospitals.
大多数关于熟能生巧假说的检验都使用了横断面数据，这些数据显示，在高手术量医院接受手术的患者术后往往有更好的结果。本研究使用纵向数据来明确检验任何一家医院的患者结果是否会随着其手术量随时间的变化而改变。
使用1990年至1993年期间魁北克所有进行髋部骨折手术的医院的纵向数据来检验手术量与结果之间的关系。纵向数据允许使用患者手术前12个月内收治医院实际进行的手术数量来衡量手术量。使用普通最小二乘法回归评估术后住院时间的决定因素，并使用逻辑回归确定住院患者死亡率的解释因素。回归包括固定效应（特定医院的虚拟变量），以控制不同医院之间随时间持续存在的结果系统差异。因此，回归模型中髋部骨折手术量的系数反映了医院内部手术量随时间变化所导致的结果差异。
固定效应是术后住院时间和住院患者死亡率的重要解释因素，表明不同医院之间的结果存在随时间持续的显著差异。在排除固定效应的回归中，手术量的系数是显著的。相比之下，当纳入固定效应时，手术量的系数不显著。
纵向数据显示，在控制了随时间固定的医院结果差异后，在一个时期内进行更多手术的医院与另一个时期相比，结果没有显著改善。这些结果不支持“熟能生巧”假说。因此，髋部骨折患者的手术量-结果关系似乎反映了高手术量医院和低手术量医院之间质量上的固定差异。
