Credibility of propensity score matching estimates. An example from Fair Trade certification of coffee producers

Propensity score matching (PSM) is an increasingly popular method for evaluation studies in agricultural and development economics. However, statisticians and econometricians have stressed that results rely on untestable assumptions, and therefore, guidelines for researchers on how to improve credibility have been developed. We follow one of these guidelines with a data set analysed by other authors to evaluate the impact of Fair Trade certification on the income of coffee producers. We provide thereby a best practice example of how to evaluate the credibility of PSM estimates. We find that a thorough assessment of the assumptions made renders the data we use not suitable for a credible PSM estimation of the effects of treatment. We conclude that the debate about the impact of Fair Trade certification would greatly benefit from a detailed reporting of credibility checking.     

What is the benefit of membership in farm producer organizations? The case of coffee producers in Peru

Empirical evidence of the benefit of farm producer organizations (FPOs) in the developing world is mounting. There is, however, no work in South America on the relationship between FPO membership and farm-level performance. We address the gap by estimating the treatment effect of FPO membership with respect to three outcomes: quantity produced, quantity sold, and price received. The empirical application focuses on the Peruvian coffee sector, where FPOs may have played an important role during the recent price crisis. A sample of approximately 9,000 survey responses from Peruvian coffee producers during the 2015–19 period is used in the analysis. Results show a positive treatment effect of FPO membership on all three farm-level outcomes. Compared to non-FPO members, FPO members produced 120–295 kg/ha more, sold 118–296 kg/ha more, and received 0.42–1.53 PEN/kg more. We also find evidence of heterogeneity in the estimated effect of FPO membership across time, farm size, and membership probability. The findings yield novel implications in terms of policy support for FPOs.     

契约农业与养殖户收入：理论线索和经验证据

契约农业是小农户衔接现代农业的有效途径,也是我国农业产业化发展的主导形式.本文构建契约农业影响养殖户收入的理论分析框架,利用610份肉牛养殖户的微观调查数据,运用倾向得分匹配法,实证检验了契约农业对养殖户收入的影响及其作用机制.参加契约农业能显著提升养殖户收入水平,销售合同和生产管理合同均能显著增加养殖户收入,其中生产管理合同的影响程度更大.组群差异分析发现,契约农业对养殖年限、养殖规模和养殖培训等不同组群养殖户收入具有异质性影响.养殖成本和养殖技术在契约农业与养殖户收入之间起到显著的中介作用,即契约农业通过规模效应和技术效应促进养殖户增收.养殖接力在契约农业对养殖户收入提升的过程中起到正向调节作用.政府应积极创造有利条件鼓励和引导契约农业的发展;根据养殖户资源禀赋特征,完善公司与养殖户利益分配机制;通过\"干中学\"效应,推进新技术的推广和应用;在契约农业中着力推广\"母畜分户饲养、仔畜集中育肥\"的接力式养殖经营方式,以推动畜牧产业的可持续、高质量发展.     

Impact of neutropenic complications on short-term disability in patients with cancer receiving chemotherapy

Abstract

Objectives: The study examined the impact of chemotherapy-induced neutropenic complications (CINC), defined as neutropenia with fever or infection, on short-term disability (STD) among cancer patients receiving chemotherapy.

Methods: The key outcome metrics were average monthly STD days and associated indirect costs. Patients with and without CINC were propensity score (PS) matched. Multivariate regressions were conducted on PS-matched cohorts to estimate the marginal impact of CINC.

Results: A total of 280 patients with CINC were PS-matched to 280 patients without CINC. Compared with matched patients, patients with CINC on average experienced 0.9 more STD day (3.2 vs. 2.3, p=0.046) and $155 more in indirect costs ($549 vs. 394, p=0.050) per month. After multivariate adjustment, patients with CINC experienced 1.0 more STD day (p=0.029), and incurred $200 more in indirect cost (p=0.016) per month.

Conclusions: Patients with CINC experience significantly greater STD leave than patients with no neutropenic complications from cancer chemotherapy. The overall study sample only included patients from large self-insured employers in the US and may not reflect the work loss experience of all employed patients in the US or other countries. Indirect costs associated with absenteeism and presenteeism were not measured.     

Choosing propensity score matching over regression adjustment for causal inference: when,why and how it makes sense

Summary

This study identified when regression adjustment fails to adjust adequately for differences in observed covariates and where propensity score matching is the only alternative.

Multivariate analysis might fail to adjust for observed confounders if:

• 1. The means of the propensity scores in the two groups are more than one-half a standard deviation apart unless distributions of the covariates in both groups are nearly symmetric, sample sizes of the two groups are approximately the same and distributions of the covariates in the two groups have similar variances;

• 2. The ratio of the propensity score variances in the two groups is significantly different from one;

• 3. The ratio of residual variances in the two groups after adjusting for the propensity score is significantly different from one.

Conducted retrospective analysis showed that the treatment effect would be an estimated $305 (or 26%) less if the misspecified outcome model had been chosen.     

创新与出口间因果关系分析——基于中国高技术产业企业数据的实证研究

使用1999—2009年我国18万家规模以上高技术产业微观企业数据,采用倾向得分匹配方法控制内生性问题,分析了企业创新与出口之间的因果关系。以产品创新衡量企业创新的估计结果表明,企业创新与出口间存在明显的因果关系:企业创新使其出口概率平均增加14%以上,企业出口使企业创新概率平均提升超过8%,从创新到出口、从出口到创新的因果关系方向均显著。区分出口强度和企业类型的估计结果显示:这种因果关系随着出口强度的增大而减弱;内资企业的创新对其出口的影响要大于外资企业;外资企业的出口对其创新的影响要大于内资企业。以研发衡量企业创新后也得到了类似结果。     

Micro‐impacts of the Brazilian Regional Development Funds: Does lending size matter?

This paper evaluates the micro‐impacts of regional development funds in Brazil—the Constitutional Financing Funds (CFF)—using fixed effects panel data models and generalized propensity score between 2000 and 2012. Assessing the industrial and commerce/services sectors using fixed effects models, the results provide weak evidence of a positive and statistically significant impact of the CFF on job creation and no statistically significant impact on labor productivity growth at the firm level. Regarding dose‐response estimates, the results present evidence of nonlinear effects after three years of financing, suggesting that the amount of subsidized credit plays an important role in creating jobs and improving firm productivity.     

产业转移对承接地与转出地的环境影响研究--基于皖江城市带承接产业转移示范区的分析

有关产业转移对承接地和转出地环境影响的研究一直存在较大争议。以皖江城市带承接产业转移示范区为分析对象,采用倾向得分匹配法评估、分析示范区建立对承接地和转出地的生态环境影响,实证得出结论：产业转移示范区的建立对承接地（皖江区域）的环境影响显著为正,而对主要转出地（长三角地区）的环境影响部分显著为正。因此,实施产业转移并不一定会使承接地的环境恶化,只要加强转移进入门槛和环境管制,承接地和转出地通过科学有效的产业转移可以实现环境“双赢”。