The paired availability design for historical controls.

B S Kramer,K S Lindeman,S G Baker

doi:10.1186/1471-2288-1-9

Abstract

BackgroundAlthough 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.MethodsA 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.ResultsWe 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.ConclusionThe paired availability design has promise for evaluating medical versus surgical interventions, in which it is difficult to recruit patients to a randomized trial.

Highlights

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
(4) Patient preferences for the medical intervention are constant over time
As we describe in more detail, the paired availability design consists of comparing outcomes in multiple hospitals or medical centers before versus after a change in availability of a medical intervention

Summary

Introduction

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. Many clinical investigators are unable to conduct a randomized trial because of excessive cost or required effort or difficulty overcoming strongly held beliefs among health care providers or patients. In these situations, a clinical investigator may consider a design and analysis based on observational data (Table 1). One common method of inference from observational data is the cohort study with an adjustment for risk factors using, for example, regression models [1] and propensity scores [2]. There are some notable exceptions, including studies of the effect of beta-carotene on cardiovascular mortality [6][7], the effect of hormone therapy on the rate of cardiovascular disease [8], the effect of epidural analgesia on the proba-

Methods

Results

Discussion

Conclusion