Baker S G, Lindeman K S, Kramer B S
Division of Cancer Prevention, National Cancer Institute, Bethesda, MD, USA.
BMC Med Res Methodol. 2001;1:9. doi: 10.1186/1471-2288-1-9. Epub 2001 Sep 26.
Although a randomized trial represents the most rigorous method of evaluating a medical intervention, some interventions would be extremely difficult to evaluate using this study design. One alternative, an observational cohort study, can give biased results if it is not possible to adjust for all relevant risk factors.
A recently developed and less well-known alternative is the paired availability design for historical controls. The paired availability design requires at least 10 hospitals or medical centers in which there is a change in the availability of the medical intervention. The statistical analysis involves a weighted average of a simple "before" versus "after" comparison from each hospital or medical center that adjusts for the change in availability.
We expanded requirements for the paired availability design to yield valid inference. (1) The hospitals or medical centers serve a stable population. (2) Other aspects of patient management remain constant over time. (3) Criteria for outcome evaluation are constant over time. (4) Patient preferences for the medical intervention are constant over time. (5) For hospitals where the intervention was available in the "before" group, a change in availability in the "after group" does not change the effect of the intervention on outcome.
The paired availability design has promise for evaluating medical versus surgical interventions, in which it is difficult to recruit patients to a randomized trial.
尽管随机试验是评估医学干预最严谨的方法，但某些干预措施采用这种研究设计进行评估极为困难。另一种方法，即观察性队列研究，如果无法对所有相关风险因素进行调整，可能会得出有偏差的结果。
一种最近开发且不太为人所知的替代方法是用于历史对照的配对可及性设计。配对可及性设计要求至少有10家医院或医疗中心，其中医疗干预的可及性发生变化。统计分析涉及对每家医院或医疗中心简单的“干预前”与“干预后”比较进行加权平均，并对可及性的变化进行调整。
我们扩展了配对可及性设计的要求以得出有效的推断。（1）医院或医疗中心服务于稳定的人群。（2）患者管理的其他方面随时间保持不变。（3）结局评估标准随时间保持不变。（4）患者对医疗干预的偏好随时间保持不变。（5）对于“干预前”组中可获得干预措施的医院，“干预后”组中可及性的变化不会改变干预对结局的影响。
配对可及性设计在评估医学与外科干预措施方面具有前景，在这类评估中很难招募患者进行随机试验。
