促進競爭是文獻中解釋分購的理由之一，競爭的程度由參與供應商的數目決定，以供應商的家數作參數。我建立一個兩期的模型，用「從做中學」的效果，將競爭的程度用成本結構的差異大小來表現，成本結構差異越大，競爭越激烈，透過模型讓競爭的程度由購買者內生控制。希望透過這一個簡單的模型檢視當廠商數目固定時，購買者會否在考量控制供應商的成本相似下採用分購策略。雖然發現在我模型的設定中，購買者考量兩期之下一定選擇不採用分購策略，但是，仍能發現只考量第二期的購買價格下促進競爭的確是購買者採用分購的原因之一。

In Paper [I], we theoretically assess green public procurement (GPP) as an environmental policy instrument and its ability to lead to the achievement of environmental objectives. Central to our analysis is the extent to which polluting firms choose to adapt to the public sector's environmental requirements and to invest in greener technologies. Our main finding is that the potential of GPP to function as an objective-effective instrument of environmental policy is limited and can actually be counterproductive. From an environmental policy point of view, it is crucial that GPP aims for environmental standards beyond just the technology of the polluting firms and that it is designed with reference to defined environmental objectives. In Paper [II], we use data on Swedish public procurement auctions for internal regular cleaning service contracts to provide novel empirical evidence regarding GPP and its effect on the potential suppliers' decision to submit a bid and their probability of being qualified for supplier selection. We find only a weak effect on supplier behavior, and this suggests that GPP, as used in practice, does not live up to its political expectations. However, several environmental criteria appear to be associated with increased complexity, as indicated by the reduced probability of a bid being qualified in the post-qualification process. As such, GPP appears to have limited or no potential to function as an environmental policy instrument. In Paper [III], I examine how GPP is organized in Sweden and how the potential suppliers respond to varying buyer market shares using data on Swedish public procurement auctions for internal regular cleaning service contracts. The level of GPP stringency is found to vary systematically across authority types, buyer market share, and political coalition in the relevant council or in Parliament. The results also indicate quite a substantial dispersion in GPP stringency, suggesting a low degree of coordination among contracting authorities when implementing the policy. After controlling for GPP stringency and other covariates, increased buyer market share is associated with a significant increase in the probability of potential suppliers submitting a bid. The European Commission encourages public authorities to split procurement contracts into multiple contracts in order to increase the competiveness of small and medium sized enterprises (SMEs). In Paper [IV], I use data from Swedish public procurement auctions for internal regular cleaning service contracts to study the effect of contract size and number of contracts on SME participation and probability of winning. The results indicate that SME participation is negatively related to both contract size and the number of contracts in the procurement. A possible interpretation is that reduced contract size in order to stimulate SME participation is counteracted by reduced incentives for them to enter into procurements with multiple contracts. Medium-sized firms are also more successful when bidding for smaller contracts relative to large firms. Nevertheless, the results indicate that the award rate for SMEs is positively correlated with the number of contracts in the procurement. / Green Public Procurement: An Efficient Environmental Policy Tool?