In this article, we explore the reasons why multiarm trials have been conducted and the design and analysis issues they involve. We point to three fundamental reasons for such designs: (1) Multiarm designs allow the estimation of “response surfaces”—that is, the variation in response to an intervention across a range of one or more continuous policy parameters. (2) Multiarm designs are an efficient way to test multiple policy approaches to the same social problem simultaneously, either to compare the effects of the different approaches or to estimate the effect of each separately. (3) Multiarm designs may allow for the estimation of the separate and combined effects of discrete program components. We illustrate each of these objectives with examples from the history of public policy experimentation over the past 50 years and discuss some design and analysis issues raised by each, including sample allocation, statistical power, multiple comparisons, and alignment of analysis with goals of the evaluation.

在本文中，我们探讨了进行多臂试验的原因及其涉及的设计和分析问题。我们指出了此类设计的三个基本原因：(1) 多臂设计允许估计“响应面”——即对一系列一个或多个连续政策参数的干预的响应变化。(2) 多臂设计是同时测试针对同一社会问题的多种政策方法的有效方法，既可以比较不同方法的效果，也可以分别估计每种方法的效果。(3) 多臂设计可能允许估计离散程序组件的单独和组合效果。