This paper complements the main experimental result reported in Takahashi et al. (Evolut Inst Econ Rev 16:357–374, 2019) to a deeper understanding of subjects’ bidding behavior under the VCG mechanism. In the experiment, there are two types of appearance of information about bidders’ valuations of the item given to them and the bids they are asked to submit: one is unit valuations and the unit bids themselves (Appearance 1) and the other is unit valuations and the unit bids multiplied by the number of units (Appearance 2). For subjects who compete with truth-telling machine bidders in multi-unit auctions, we confirmed that in Appearance 1, they choose truth-telling bids more frequently, and efficient allocations are observed more frequently, as compared to the situation where they compete with human bidders. This result suggests a possibility that in Appearance 1, subjects learn their dominant strategy not by practicing with other subjects but by practicing with machine bidders in experiments for multi-unit auctions, although the item allocation and payment determination under the VCG mechanism is never intuitively understandable to the subjects.

本文是对Takahashi等人报道的主要实验结果的补充。（Evolut Inst Econ修订版16：357–374，2019），以更深入地了解VCG机制下主体的竞标行为。在实验中，关于投标人对他们提供的项目的估价和要求他们提交的投标的信息的出现有两种类型：一种是单位估价，单位是自己投标（外观1），另一种是单位估价。单位出价乘以单位数（外观2）。对于在多单位竞标中与真相竞标者竞争的主体，我们确认在出场一中，与与人类竞争的情况相比，他们更频繁地选择真相竞标，并且更频繁地观察到有效分配投标人。