公部門與私部門提供的公共財同時存在時的排擠效果的實驗研究

An Experimental Study on the Crowding-Out Effect with Both Publicly and Privately Provided Public Goods

排擠效果的理論和實驗文獻通常假設租稅和自願性捐獻用來融通「同一」公共財。基於此一假設，不論是純粹利他還是不純粹利他的理論模型皆預期租稅會排擠自願性捐獻，而無法解釋租稅會擠入（增加）自願性捐獻的結果。本實驗研究檢驗公部門和私部門提供的公共財同時存在時的排擠效果。本文發現當公部門和私部門提供的公共財對實驗參與者有同等價值時，或當公部門提供的公共財較私部門提供的公共財有價值時，傳統的排擠效果會發生。然而當私部門提供的公共財叫公部門提供的公共財有價值時，則有擠入效果，亦即租稅不僅不會降低自願性捐獻，還會增加更多的自願性捐獻。

The theoretical and experimental literature on crowding-out usually assumes that taxes and voluntary contributions are used to fund the “same” public good. Based on this assumption, theoretical models of both pure and impure altruism predict a result of crowding-out that is unable to explain an outcome of crowding-in. This experimental study examines the crowding-out effect when both publicly and privately provided public goods are present. It is found that when both publicly and privately provided public goods are equally valuable to subjects, or when the former is more valuable than the latter, the traditional results of crowding-out occur. However, crowding-in is present if the privately provided public good is more valuable than the publicly provided public good.