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On the Treatment of Heteroscedasticity in Crop Yield Data

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  • Alan P Ker
  • Tor N Tolhurst

Abstract

In empirical applications with crop yield data, conditioning for heteroscedasticity is both important and challenging. It is important because the scale of the distribution can markedly influence the results, and challenging because statistical tests for the common heteroscedasticity assumptions (constant or proportional variance) often lead to ambiguous conclusions. Alternatively, Harri et al. (2011) proposed a methodology that estimates the degree of heteroscedasticity, removing the need to make a specific assumption. Such approaches assume that volatility changes are symmetric (identical) across tails of the yield distribution. We propose a generalization to the Harri et al. (2011) methodology, which allows asymmetry between the tails, akin to the generalization of GARCH to AGARCH. Using U.S. county level yield data from 1951–2017, we find evidence of asymmetry in corn and soybean, but not wheat. Moreover, the asymmetry takes a particular form—increasing volatility in the lower tail. To investigate economic significance, we consider the effect of imposing symmetric heteroscedasticity in rating crop insurance contracts, as currently done by the USDA’s Risk Management Agency in rating their Area Risk Protection products. We find that relaxing the symmetry assumption leads to economically and statistically significant rents. Our results suggest that the Risk Management Agency and others should consider the possibly asymmetric nature of heteroscedasticity in crop yield data.

Suggested Citation

  • Alan P Ker & Tor N Tolhurst, 2019. "On the Treatment of Heteroscedasticity in Crop Yield Data," American Journal of Agricultural Economics, Agricultural and Applied Economics Association, vol. 101(4), pages 1247-1261.
  • Handle: RePEc:oup:ajagec:v:101:y:2019:i:4:p:1247-1261.
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    File URL: http://hdl.handle.net/10.1093/ajae/aaz004
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    Citations

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    Cited by:

    1. Matthew Stuart & Cindy Yu & David A. Hennessy, 2023. "The Impact of Stocks on Correlations between Crop Yields and Prices and on Revenue Insurance Premiums using Semiparametric Quantile Regression," Papers 2308.11805, arXiv.org, revised Jun 2024.
    2. Bucheli, Janic & Dalhaus, Tobias & Finger, Robert, 2022. "Temperature effects on crop yields in heat index insurance," Food Policy, Elsevier, vol. 107(C).
    3. repec:ags:aaea22:335759 is not listed on IDEAS
    4. Yong Liu & Alan P. Ker, 2021. "Simultaneous borrowing of information across space and time for pricing insurance contracts: An application to rating crop insurance policies," Journal of Risk & Insurance, The American Risk and Insurance Association, vol. 88(1), pages 231-257, March.
    5. Arora, Gaurav & Agarwal, Sandip K., 2020. "Agricultural input use and index insurance adoption: Concept and evidence," 2020 Annual Meeting, July 26-28, Kansas City, Missouri 304508, Agricultural and Applied Economics Association.
    6. Yong Liu & A. Ford Ramsey, 2023. "Incorporating historical weather information in crop insurance rating," American Journal of Agricultural Economics, John Wiley & Sons, vol. 105(2), pages 546-575, March.
    7. Chemeris, Anna & Liu, Yong & Ker, Alan P., 2022. "Insurance subsidies, climate change, and innovation: Implications for crop yield resiliency," Food Policy, Elsevier, vol. 108(C).
    8. Hengli Wang & Hong Liu & Danyang Wang, 2022. "Agricultural Insurance, Climate Change, and Food Security: Evidence from Chinese Farmers," Sustainability, MDPI, vol. 14(15), pages 1-17, August.
    9. Belasco, Eric J., 2020. "WAEA Presidential Address: Moving Agricultural Policy Forward: Or, There and Back Again," Journal of Agricultural and Resource Economics, Western Agricultural Economics Association, vol. 45(3), September.
    10. Jing Yi & Samantha Cohen & Sarah Rehkamp & Patrick Canning & Miguel I. Gómez & Houtian Ge, 2023. "Overcoming data barriers in spatial agri‐food systems analysis: A flexible imputation framework," Journal of Agricultural Economics, Wiley Blackwell, vol. 74(3), pages 686-701, September.
    11. Xiaotao Li & Jinzheng Ren & Beibei Niu & Haiping Wu, 2020. "Grain Area Yield Index Insurance Ratemaking Based on Time–Space Risk Adjustment in China," Sustainability, MDPI, vol. 12(6), pages 1-15, March.

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