Research

Working Papers

• Etumnu, C. E. (2026). Online Demand for Credence Foods: Evidence from Organic and Non-GMO Beverages on Amazon. Under review at Food Policy. 

Abstract: Although a large literature examines consumer demand for credence foods in traditional retail settings, much less is known about how such demand extends to digital marketplaces. This paper investigates how organic and Non-GMO certification labels shape consumer demand in online food retail markets. Using high-frequency, product-level data from the tea and coffee categories on Amazon in the United Kingdom (UK) and the United States (US), I estimate the influence of verified certification labels on product demand and the responsiveness of demand to price changes across heterogeneous products. The results show that organic and Non-GMO beverages command a significant sales premium, averaging approximately 12 percent. This premium varies across the sales distribution, ranging from about 8 percent at the 25th sales quantile to roughly 25 percent at the 75th quantile. Demand for certified beverages is also substantially less price-elastic, suggesting stronger consumer loyalty and greater pricing power for certified products in digital markets. The estimated demand patterns vary systematically across countries (UK vs. US), product types (tea vs. coffee), and seller types (Amazon vs. third-party sellers). Overall, the findings provide new evidence on how credence labels drive product differentiation and pricing strategies in rapidly expanding online food retail markets.

• Etumnu, C. E. (2026). The Value of Brand Variety: Evidence from Amazon’s Beverage Markets. Revise and Resubmit at Agribusiness: An International Journal.  

Abstract: In online marketplaces, where consumers face information asymmetry and high search costs, brand recognition serves as a powerful heuristic. Yet, relative to well-studied signals like consumer reviews and ratings, theoretical and empirical evidence on the role of brands remains limited. This paper addresses this gap by examining the impact of intra-brand product variety on performance in Amazon's beverage categories in the United Kingdom and the United States. We introduce the Brand Variety Score (BVS), measured as a brand's share of product listings within a narrowly defined product category, capturing the depth of its assortment. Drawing on high-frequency panel data, we exploit within-product and within-brand variation and employ fixed-effects regressions, copula-based models, and instrumental variables to mitigate endogeneity concerns. Our preferred estimates indicate that a 1 percent increase in BVS is associated with a 0.09% reduction in beverage prices and a 0.27% increase in beverage sales. These effects, when extrapolated across Amazon's marketplace, imply substantial consumer welfare gains of about $71 million, but approximately no gain in producer surplus. We further show that these benefits arise primarily through economies of scale and scope that reduce costs on the supply side, and through stronger quality signaling and passed-through cost reductions on the demand side. Our findings thus highlight BVS as a valuable complement to existing metrics of market competition, such as the Herfindahl–Hirschman index, offering key insights for platform owners and their third-party sellers. 

• Etumnu, C. E. and Foster, K. (2026). Does Fulfillment by Amazon boost the Reputation of Grocery Sellers?  Revise and Resubmit at the Journal of Agricultural Economics.

Abstract: In 2006, Amazon launched the Fulfillment by Amazon (FBA) program, providing support to third-party sellers for a fee. While the program has the potential to enhance sellers' reputations, evidence regarding its effectiveness is limited. This study estimates the impact of FBA usage on seller reputation, measured by the average star rating a seller receives. Using 26 weeks of panel data from Canada, the United Kingdom, and the United States, three key findings emerge from fixed effects and staggered adoption estimation approaches. First, using FBA significantly boosts a seller's reputation, leading to higher average ratings in the short term than in the long term. This improvement is mainly due to FBA's competitive advantages, such as eligibility for Amazon Prime, standardized fulfillment quality, and excellent customer service. Second, although FBA impacts are positive in every country, we find cross-country heterogeneity in effect sizes and significance levels, with the largest effects in Canada. Third, we show that large sellers have the best reputation, and all sellers benefit from the FBA program. However, medium-sized sellers benefit the most from the program. This trend can be attributed to how the benefits of the FBA program accrue optimally to sellers based on their operational scale. These results suggest that the FBA program is indeed effective in enhancing seller reputation, with implications for third-party sellers, Amazon, and regulators.

• Etumnu, C. E. (2026). The Paradox of Brand Variety: Effects on Product Quality in Amazon's Marketplace. Under review at Agribusiness: An International Journal. 

Abstract: This paper examines how brand variety—the number of products offered within a brand—affects perceived and operational product quality in digital marketplaces. We construct a Brand Variety Score (BVS), defined as the share of a brand’s products relative to the total number of products in its category, and estimate its causal effects on two dimensions of quality: consumer perceptions, measured by average star ratings, and operational performance, measured by stockout rates. Using high-frequency panel data on black tea and ground coffee products sold on Amazon.com, we find that a 10 percent increase in BVS raises perceived quality by 0.05 percent but reduces operational quality by 0.24 percent. Instrumental variable estimates using lagged BVS confirm that these effects are not driven by reverse causality or unobserved brand heterogeneity. The results indicate that product proliferation operates as a costly signal that enhances consumer trust and algorithmic visibility while imposing managerial and logistical frictions. The findings highlight a paradox—the dual role of brand variety as both a strategic complement and an operational constraint in multiproduct platform competition.

Publications

(14) Etumnu, C. E. (2025). Subscribe and Save: Evaluating the Effectiveness of Amazon’s Subscription Program. Agribusiness. https://doi.org/10.1002/agr.22052. 

(13) Etumnu, C. E.,  Cherinades, L., & Jaenicke, E. (2025). Grocery Stockouts and Seller Performance in Amazon's Marketplaces. Agribusiness. https://doi.org/10.1002/agr.22051. 

(12) Etumnu, C. E., Edobor, E., & Marshall, M. (2024). Impact of FTC’s Allegation on Amazon’s Marketplace: Evidence from Coffee Products. Agribusiness. https://doi.org/10.1002/agr.21996. 

(11) Etumnu, C. E. & Malone, T. (2024). An Empirical Examination of BuyBox Assignments in Online Grocery Retail. Agribusiness. https://doi.org/10.1002/agr.21978.  

(10) Etumnu, C. E. & Noumir, A. (2024). The Effect of Amazon Prime on Sales Ranks. Journal of Food Distribution Research.

(9) Etumnu, C. E. & Volpe, R. J. (2024). Measuring Brand Equity on Amazon.com: The Case of Starbucks. Journal of Food Distribution Research. Volume 55, Issue 1, pp. 15-31.

(8) Etumnu, C. E., Wang, T., Jin, H., Schad, J., Sieverding, H., & Clay, D. (2023). Understanding Farmers’ Perception of Extreme Weather Events and Adaptive Measures. Climate Risk Management, 100494.   https://doi.org/10.1016/j.crm.2023.100494. 

(7) Quagrainie, K., de Souza, S. V., Athnos, A., Etumnu, C.E., Knudson, W., Kinnunen, R., & Hitchens, P. (2023). The seafood basket: Application of zero-inflated model to fish count purchase. Aquaculture, 565, 739097. 

(6) Etumnu, C. E. (2022). A Competitive Marketplace or an Unfair Competitor? An Analysis of Amazon and its Best Sellers Ranks. Journal of Agricultural Economics.  DOI.10.1111/1477-9552.12495.

(5) Etumnu, C. E. (2022). Free Shipping. Applied Economic Letters. DOI: 10.1080/13504851.2022.2094871.

(4) Athnos, A., de Souza, S. V., Quagrainie, K., Etumnu, C. E., Knudson, W., Kinnunen, R. E., & Hitchens, P. (2022). Are US consumers willing to pay more by the lake? An analysis of preferences for Great Lakes region fish. Agricultural and Resource Economics Review, 1-26.

(3) Etumnu, C. E., Foster, K., Widmar, N. O., Lusk, J. L., & Ortega, D. L. (2020).  Does the Distribution of Online Ratings affect Sales? Evidence from Amazon. Agribusiness. Vol. 36(4): 501-521.

(2) Etumnu, C. E., & Gray, A. W. (2020). A Clustering Approach to Understanding Farmers' Success Strategies. Journal of Agricultural and Applied Economics, 1-17.

(1) Etumnu, C. E. & Widmar, N. O. (2020). Grocery Shopping in the Digital Era. Choices, Vol. 35(2):1-8.