Objectives

Due to time and financial limitations, most randomized controlled trials (RCTs) are conducted employing non-random sampling techniques. Although valuable, when the unique characteristics of a non-random sample unknowingly interact with the treatment, the results of the RCT could become biased. Nevertheless, the amount of bias remains unexamined.

Methods

The current study evaluated if non-random sampling techniques could bias the slope coefficients of an RCT when an interaction exists between the treatment and a characteristic in the population using two simulation analyses.

Results

The results suggested that the sampling distributions of slope coefficients from an RCT — across random specifications — expand drastically when (1) an interaction between the treatment and a characteristic in the population exists and (2) the non-random sample has unique scores on that characteristic.

Conclusions

Considering these findings, four recommendations are made for scholars currently or intending to conduct a RCT employing non-random sampling techniques.

中文翻译：

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人口特征的调节作用：使用非随机样本进行实验研究时的潜在偏差因素

目标

由于时间和财务限制，大多数随机对照试验 (RCT) 都是采用非随机抽样技术进行的。尽管很有价值，但当非随机样本的独特特征在不知不觉中与治疗相互作用时，RCT 的结果可能会出现偏差。尽管如此，偏差的数量仍然未经审查。

方法

当前的研究使用两种模拟分析评估了当治疗与人群中的特征之间存在相互作用时，非随机抽样技术是否会使 RCT 的斜率系数产生偏差。

结果

结果表明，当 (1) 治疗与总体特征之间存在相互作用以及 (2) 非随机样本在这方面具有唯一分数时，RCT 中斜率系数的抽样分布（跨随机规范）会急剧扩大特征。

结论

考虑到这些发现，对目前或打算使用非随机抽样技术进行 RCT 的学者提出了四项建议。