環境價值評估中廣泛存在支付工具效應,經濟學家發現,當采用"繳稅"和"勞動"支付工具分別開展環境價值評估時,得到的評估結果往往存在顯著差異,但現有研究仍未對支付工具效應形成的原因進行解釋。該研究同時采用"繳稅"和"勞動"兩種支付工具設計選擇實驗,對北京市城市濕地價值進行評估,并檢驗兩種支付工具的評估結果是否存在差異。該研究首先基于時間分配理論比較了"繳稅"和"勞動"支付工具在評估環境價值時存在的理論差異,并據此提出了研究假說。隨后,課題組分別基于兩種支付工具設計了兩組選擇實驗,在2017年5月對北京市居民開展了網絡調查,調查對象被隨機分配到兩組實驗樣本中。基于調查數據,該研究采用隨機參數Logit模型和廣義多元Logit模型分析了北京市居民對濕地屬性的偏好,并據此估算了濕地屬性的邊際價值。結果顯示,北京市濕地面積每增加1 000 hm2、濕地Ⅱ類與Ⅲ類水質的占比每增加1%、濕地動植物種類每增加10種、濕地植被覆蓋率每增加1%,基于"繳稅"支付工具估算的邊際支付意愿分別為每年23.254元、17.266元、5.559元和9.041元,基于"勞動"支付工具估算的邊際勞動意愿分別為每年0.211 d、0.138 d、0.042 d和0.093 d。采用繳稅支付工具估算的邊際支付意愿約為采用勞動支付工具估算的邊際勞動意愿與實際工資率乘積的50%,即支付工具效應得到證實。男性樣本中的支付工具效應強于女性樣本。而且,工資性收入在總收入中的占比越高,支付工具效應越強。該研究的分析結論可以為城市濕地的修復與保護提供必要的決策參考。后續的研究者和政策制定者可以考慮利用支付工具效應設計環境政策,從而進一步提高社會福利。

Payment vehicle effect( PVE) extensively exists in measuring environmental values,i. e. economists verified remarkable difference of valuation outcome between‘tax’vehicle and‘labor’vehicle. But previous studies have not discovered why PVE existed.This paper uses both ‘tax’and ‘labor’vehicles to evaluate urban wetlands in Beijing,and further to explore the existence of PVE.We firstly compare the theoretical difference,on the basis of time allocation theory,between monetary and labor vehicles when evaluating urban wetlands,and accordingly propose our hypotheses. ‘Tax’and ‘labor’vehicles are respectively used to design two separate choice experiments,and then we conduct an online survey on Beijing residents in May,2017,and respondents are randomly allocated in the two experiments. We use random parameter Logit model and generalize multinomial Logit model to elicit marginal values of four different wetland attributes. Results indicate that,mean marginal willingness-to-pay values elicited through tax vehicle for wetland size( every 1 000 hm2),proportion of class Ⅱ and Ⅲ water quality( one percent),number of animal and plant species( every 10 species),vegetation coverage( one percent) are respectively annually RMB 23.254 RMB 17.266,RMB 5.559 and RMB 9.041,while mean marginal willingness-to-work values elicited through labor vehicle are respectively annually 0.211 day,0.138 day,0.042 day and 0.093 day. Significant PVE is confirmed in urban wetland valuation,where the marginal willingness-to-pay values elicited through tax vehicle is only about 50% of those elicited by‘labor’vehicle( i.e. product of willingness-to-work and wage rate). PVE is stronger in male samples than in female samples. And the higher the proportion of wage income in total income,the larger is PVE.Above results might offer essential reference for the restoration and protection of urban wetlands. Researchers and practitioners,in the future,could take PVE into consideration when designing environmental policies in order to further improve social welfare.