Price convergence in grain markets with seasonal differences

Michael Olabisi; Jiawen Liu; Toyin Ajibade; Mywish K. Maredia

doi:10.1371/journal.pone.0339577

Peer Review History

Original SubmissionJune 8, 2025
17 Jul 2025 Decision Letter - Eugenio Sebastian Antonio Bobenrieth, Editor PONE-D-25-30518 Price Convergence in Grain Markets with Seasonal Differences PLOS ONE Dear Dr. Olabisi, Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process. Please submit your revised manuscript by Aug 31 2025 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file. 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Additional Editor Comments: Reviewer 1: This is a clearly-written and straightforward article using agricultural price data collected from 97 markets in Nigeria to show that locally-produced crops (rice and cowpea) experience faster price convergence across markets when both markets are in the harvest season. The analysis is based on reduced-form correlations. It would benefit from a better theoretical discussion of price behavior under storage costs (which explain low harvest prices that then increase throughout the year) and trade costs (e.g. under what conditions markets are segmented vs. trading) as this would help us understand the results and their implications. However, I think that is probably beyond the scope of this short article. Here are some minor comments that I think should be addressed: 1) Please provide more information on the markets. How were they selected? Can you show them on a map? How many are in the South and how many in the North? (This seems to be the key division in terms of your harvest seasons in table 5.) 2) You should reference the table 2 results in the main paper. One of the reasons why the Harvest to Non-Harvest price gaps appear larger in table 1 is that markets with different harvest seasons (North vs. South) are further apart. 3) P. 13 / table 3: if I am reading the table correctly, the “Harvest to Non-Harvest” category is NOT the slowest for White Cowpea as you state in the text. It is only the slowest for Rice. 4) Appendix 1.a.: you should show the comparison that you did with the FEWS NET data. Also, please explain what is shown in figures 2 and 3 – is this your data or the FEWS NET data? 5) Typos to fix: The first sentence of section II has a double “and”; in table 1 the last row should be non-harvest to non-harvest. 6) Your statement that the data are available from the authors to academic researchers upon request does not satisfy this journal’s data policy as I understand it. You should make the data publicly available to all in an online repository. ---- Reviewer 2: 1. Originality and significance of contribution to existing knowledge This paper investigates the impact of seasonal harvest timing on price convergence for staple grains across 97 Nigerian markets. The authors leverage weekly price data to argue that market integration is not merely a function of spatial factors but is critically mediated by the temporal synchrony of production cycles. Nevertheless, the empirical narrative largely confirms what the arbitrage condition already predicts (i.e., larger contemporaneous supplies compress gaps, asynchronous supplies widen them). 2. Appropriateness of the abstract as a description of the paper The abstract clearly states the objective, dataset (weekly prices from 97 markets), and headline findings (faster convergence in synchronous harvests, slower in asynchronous ones). However, it provides no hint of the methodological framework. 3. Adequacy of the literature review The authors successfully position their work within the existing literature on market integration, price transmission, and food security in Africa. The manuscript correctly references foundational and contemporary studies, effectively differentiating its temporal focus from prior work centered on spatial frictions. Yet the review leans heavily on sources published before 2020. 4. Organization and readability The paper is logically structured, following a standard format that is easy to follow. The writing is generally clear. In Table 1, the variable "Average Price Gap (Harvest to Harvest)" is duplicated. Also, the authors reveals that the x-axis from Figure 1 is based only on the rainy season harvest, but does not explain why. 5. Soundness of methodology, analysis, and interpretation The core methodological approach is suited to the research question. However, there are some concerns: - the manuscript first states that “all data are fully available without restriction” and later that data “are available from the authors on request”; this is a contradiction; - the authors acknowledge that their network data on market connections is not crop-specific, which introduces potential noise into the analysis; - weekly prices offer granularity, yet the sample spans only 14 months (Feb 2022–Apr 2023); one harvest cycle could be insufficient to assess structural seasonal effects, macro shocks, or policy interventions; - standard unit-root and cointegration tests should precede the regression; 6. Evidence supports conclusions. The main conclusions are supported by the regression results. However, the paper lists no explicit limitation section. [Note: HTML markup is below. Please do not edit.] Reviewers' comments: Reviewer's Responses to Questions Comments to the Author 1. Is the manuscript technically sound, and do the data support the conclusions? The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented. Reviewer #1: Yes Reviewer #2: Yes ******** 2. Has the statistical analysis been performed appropriately and rigorously? Reviewer #1: Yes Reviewer #2: Yes ****** 3. Have the authors made all data underlying the findings in their manuscript fully available? The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified. Reviewer #1: No Reviewer #2: No ****** 4. Is the manuscript presented in an intelligible fashion and written in standard English? PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here. Reviewer #1: Yes Reviewer #2: Yes ****** 5. Review Comments to the Author Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters) Reviewer #1: This is a clearly-written and straightforward article using agricultural price data collected from 97 markets in Nigeria to show that locally-produced crops (rice and cowpea) experience faster price convergence across markets when both markets are in the harvest season. The analysis is based on reduced-form correlations. It would benefit from a better theoretical discussion of price behavior under storage costs (which explain low harvest prices that then increase throughout the year) and trade costs (e.g. under what conditions markets are segmented vs. trading) as this would help us understand the results and their implications. However, I think that is probably beyond the scope of this short article. Here are some minor comments that I think should be addressed: 1) Please provide more information on the markets. How were they selected? Can you show them on a map? How many are in the South and how many in the North? (This seems to be the key division in terms of your harvest seasons in table 5.) 2) You should reference the table 2 results in the main paper. One of the reasons why the Harvest to Non-Harvest price gaps appear larger in table 1 is that markets with different harvest seasons (North vs. South) are further apart. 3) P. 13 / table 3: if I am reading the table correctly, the “Harvest to Non-Harvest” category is NOT the slowest for White Cowpea as you state in the text. It is only the slowest for Rice. 4) Appendix 1.a.: you should show the comparison that you did with the FEWS NET data. Also, please explain what is shown in figures 2 and 3 – is this your data or the FEWS NET data? 5) Typos to fix: The first sentence of section II has a double “and”; in table 1 the last row should be non-harvest to non-harvest. 6) Your statement that the data are available from the authors to academic researchers upon request does not satisfy this journal’s data policy as I understand it. You should make the data publicly available to all in an online repository. Reviewer #2: 1. Originality and significance of contribution to existing knowledge This paper investigates the impact of seasonal harvest timing on price convergence for staple grains across 97 Nigerian markets. The authors leverage weekly price data to argue that market integration is not merely a function of spatial factors but is critically mediated by the temporal synchrony of production cycles. Nevertheless, the empirical narrative largely confirms what the arbitrage condition already predicts (i.e., larger contemporaneous supplies compress gaps, asynchronous supplies widen them). 2. Appropriateness of the abstract as a description of the paper The abstract clearly states the objective, dataset (weekly prices from 97 markets), and headline findings (faster convergence in synchronous harvests, slower in asynchronous ones). However, it provides no hint of the methodological framework. 3. Adequacy of the literature review The authors successfully position their work within the existing literature on market integration, price transmission, and food security in Africa. The manuscript correctly references foundational and contemporary studies, effectively differentiating its temporal focus from prior work centered on spatial frictions. Yet the review leans heavily on sources published before 2020. 4. Organization and readability The paper is logically structured, following a standard format that is easy to follow. The writing is generally clear. In Table 1, the variable "Average Price Gap (Harvest to Harvest)" is duplicated. Also, the authors reveals that the x-axis from Figure 1 is based only on the rainy season harvest, but does not explain why. 5. Soundness of methodology, analysis, and interpretation The core methodological approach is suited to the research question. However, there are some concerns: - the manuscript first states that “all data are fully available without restriction” and later that data “are available from the authors on request”; this is a contradiction; - the authors acknowledge that their network data on market connections is not crop-specific, which introduces potential noise into the analysis; - weekly prices offer granularity, yet the sample spans only 14 months (Feb 2022–Apr 2023); one harvest cycle could be insufficient to assess structural seasonal effects, macro shocks, or policy interventions; - standard unit-root and cointegration tests should precede the regression; 6. Evidence supports conclusions. The main conclusions are supported by the regression results. However, the paper lists no explicit limitation section. ****** 6. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files. If you choose “no”, your identity will remain anonymous but your review may still be made public. Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy. Reviewer #1: No Reviewer #2: No ******** [NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.] While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. 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Revision 1
12 Sep 2025 Author Response Reviewer 1(R1): This is a clearly-written and straightforward article using agricultural price data collected from 97 markets in Nigeria to show that locally-produced crops (rice and cowpea) experience faster price convergence across markets when both markets are in the harvest season. The analysis is based on reduced-form correlations. It would benefit from a better theoretical discussion of price behavior under storage costs (which explain low harvest prices that then increase throughout the year) and trade costs (e.g. under what conditions markets are segmented vs. trading) as this would help us understand the results and their implications. However, I think that is probably beyond the scope of this short article. Response to Reviewer (RtoR): We appreciate the reviewer’s suggestion to strengthen the theoretical discussion of price dynamics under storage and trade costs. In the revised manuscript, we have added a concise theoretical section that draws on the storage model (e.g., Williams and Wright, 1991; Wright, 2011) to explain how storage costs influence seasonal price patterns, and on standard trade cost frameworks (e.g., Samuelson, 1952) to clarify the conditions under which markets are segmented versus integrated. This additional discussion provides a clearer conceptual foundation for interpreting our empirical results, while keeping the focus and length appropriate for a short article. R1: Here are some minor comments that I think should be addressed: 1) Please provide more information on the markets. How were they selected? Can you show them on a map? How many are in the South and how many in the North? (This seems to be the key division in terms of your harvest seasons in table 5.) RtoR: We appreciate the reviewer’s suggestion. The revised manuscript now includes additional details on the selection of the 97 markets (Section 2: Page 3) and a new map (Figure 1) showing their locations. The map also indicates whether each market is in the North or South, as this distinction is important for understanding harvest seasonality. Of these markets, 61 are in the North and 36 are in the South. R1: 2) You should reference the table 2 results in the main paper. One of the reasons why the Harvest to Non-Harvest price gaps appear larger in table 1 is that markets with different harvest seasons (North vs. South) are further apart. RtoR: Thank you for pointing this out. We have revised the manuscript to reference the Table 2 results in the main text and now explicitly note that part of the larger Harvest to Non-Harvest price gaps in Table 1 may reflect the greater distance between markets in the North and South. (last paragraph of Page 4) R1: 3) P. 13 / table 3: if I am reading the table correctly, the “Harvest to Non-Harvest” category is NOT the slowest for White Cowpea as you state in the text. It is only the slowest for Rice. RtoR: Thank you for catching this inconsistency. You are correct—the “Harvest to Non-Harvest” category is the slowest only for rice. We have revised the text to accurately reflect the results for white cowpea in Table 3. R1: 4) Appendix 1.a.: you should show the comparison that you did with the FEWS NET data. Also, please explain what is shown in figures 2 and 3 – is this your data or the FEWS NET data? RtoR: Thank you for the suggestion. We have updated Appendix 1.a to include the comparison with FEWS NET data. Figures 2 and 3 now clearly indicate their respective data sources—Figure 2 uses our market price survey data, while Figure 3 is based on FEWS NET prices. We have also added a brief discussion in the appendix explaining the observed patterns and noting that, despite differences in coverage and time span, the seasonal trends are broadly consistent, serving as a robustness check for our data. R1: 5) Typos to fix: The first sentence of section II has a double “and”; in table 1 the last row should be non-harvest to non-harvest. RtoR: Thank you for pointing these out. We have corrected the double “and” in the first sentence of Section II and fixed the label in the last row of Table 1 to read “Non-Harvest to Non-Harvest.” R1: 6) Your statement that the data are available from the authors to academic researchers upon request does not satisfy this journal’s data policy as I understand it. You should make the data publicly available to all in an online repository. ---- RtoR: We appreciate this important clarification. In line with the journal’s data policy, we have now made both the dataset and replication code publicly available through an online repository on GitHub: [link]. We have updated the Data Availability Statement in the appendix to reflect this change. Reviewer 2 (R2): 1. Originality and significance of contribution to existing knowledge This paper investigates the impact of seasonal harvest timing on price convergence for staple grains across 97 Nigerian markets. The authors leverage weekly price data to argue that market integration is not merely a function of spatial factors but is critically mediated by the temporal synchrony of production cycles. Nevertheless, the empirical narrative largely confirms what the arbitrage condition already predicts (i.e., larger contemporaneous supplies compress gaps, asynchronous supplies widen them). RtoR: We appreciate the reviewer’s observation. Thank you for the summary. R2: 2. Appropriateness of the abstract as a description of the paper The abstract clearly states the objective, dataset (weekly prices from 97 markets), and headline findings (faster convergence in synchronous harvests, slower in asynchronous ones). However, it provides no hint of the methodological framework. RtoR: We thank the reviewer for pointing this out. We have revised the abstract to briefly mention the methodological framework, noting that our results are obtained from a dyadic panel regression of price-gap dynamics across market pairs classified by seasonal harvest alignment. R2: 3. Adequacy of the literature review The authors successfully position their work within the existing literature on market integration, price transmission, and food security in Africa. The manuscript correctly references foundational and contemporary studies, effectively differentiating its temporal focus from prior work centered on spatial frictions. Yet the review leans heavily on sources published before 2020. RtoR: We appreciate the reviewer’s positive assessment of our positioning within the literature. We agree that incorporating more recent studies would strengthen the review. Accordingly, we have added references to several relevant works published after 2020, particularly those addressing seasonal dynamics and market integration in African contexts. R2: 4. Organization and readability The paper is logically structured, following a standard format that is easy to follow. The writing is generally clear. In Table 1, the variable "Average Price Gap (Harvest to Harvest)" is duplicated. Also, the authors reveal that the x-axis from Figure 1 is based only on the rainy season harvest, but does not explain why. RtoR: We thank the reviewer for the positive comments on the paper’s structure and clarity. We have corrected the duplication of the “Average Price Gap (Harvest to Harvest)” variable in Table 1, this was a typo, which we have fixed. Regarding Figure 1(Figure 2 in our updated manuscript), we now clarify in the footnotes that the x-axis is anchored to the end of the rainy-season harvest to ensure consistency across markets, as the dry-season harvest occurs in fewer locations and roughly six months later. R2: 5. Soundness of methodology, analysis, and interpretation The core methodological approach is suited to the research question. However, there are some concerns: - the manuscript first states that “all data are fully available without restriction” and later that data “are available from the authors on request”; this is a contradiction; - the authors acknowledge that their network data on market connections is not crop-specific, which introduces potential noise into the analysis; - weekly prices offer granularity, yet the sample spans only 14 months (Feb 2022–Apr 2023); one harvest cycle could be insufficient to assess structural seasonal effects, macro shocks, or policy interventions; - standard unit-root and cointegration tests should precede the regression; RtoR: We thank the reviewer for these helpful observations. We have addressed each point as follows: Data availability statement – We have resolved the inconsistency by making both the code and data publicly available via our GitHub repository [link] and updating the statement accordingly. Network data crop-specificity – While the network links are not crop-specific, the crops we study are available in almost all markets (cowpea and local rice in all markets, long-grain rice in 90 of 97 markets). These links are only used to restrict the sample to connected markets and are not included as regressors. We acknowledge this as a potential source of noise and have explicitly noted it in the limitations section. Sample period limitation – We acknowledge the short 14-month span and have added this to our limitations section, noting that future work using longer time series could better capture structural seasonal patterns, macroeconomic shocks, or policy interventions. Unit-root and cointegration tests – We now report Maddala–Wu panel unit-root tests in the appendix and confirm that the price gap variables are stationary before running the regressions. R2: 6. Evidence supports conclusions. The main conclusions are supported by the regression results. However, the paper lists no explicit limitation section. RtoR: We thank the reviewer for this suggestion. We have now added an explicit Limitations section to the manuscript, outlining key constraints such as the non–crop-specific nature of the network data, the limited 14-month sample period, and the potential influence of unobserved local factors. Attachments Attachment Submitted filename: R & R - Plos One.docx https://doi.org/10.1371/journal.pone.0339577.r002
19 Nov 2025 Decision Letter - Eugenio Sebastian Antonio Bobenrieth, Editor PONE-D-25-30518R1 Price Convergence in Grain Markets with Seasonal Differences PLOS ONE Dear Dr. Olabisi, Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process. In particular pay attention to the comments of Reviewer #1 to equations, they are important to clearly identify your contribution. Please submit your revised manuscript by Jan 02 2026 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file. Please include the following items when submitting your revised manuscript: A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'. A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'. An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'. If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter. If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: https://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols. Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols. We look forward to receiving your revised manuscript. Kind regards, Eugenio Sebastian Antonio Bobenrieth, Ph.D. Academic Editor PLOS ONE Journal Requirements: If the reviewer comments include a recommendation to cite specific previously published works, please review and evaluate these publications to determine whether they are relevant and should be cited. There is no requirement to cite these works unless the editor has indicated otherwise. Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice. [Note: HTML markup is below. Please do not edit.] Reviewers' comments: Reviewer's Responses to Questions Comments to the Author 1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation. Reviewer #1: (No Response) Reviewer #2: All comments have been addressed ******** 2. Is the manuscript technically sound, and do the data support the conclusions? The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented. Reviewer #1: Yes Reviewer #2: Yes ****** 3. Has the statistical analysis been performed appropriately and rigorously? Reviewer #1: Yes Reviewer #2: Yes ****** 4. Have the authors made all data underlying the findings in their manuscript fully available? The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified. Reviewer #1: Yes Reviewer #2: Yes ****** 5. Is the manuscript presented in an intelligible fashion and written in standard English? PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here. Reviewer #1: Yes Reviewer #2: Yes ****** 6. Review Comments to the Author Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters) Reviewer #1: Thank you for addressing my comments. I have some last minor points (numbers refer to my numbered comments on the previous version): 0) The new section on the Theoretical Framework is helpful. However, there are two points of confusion. First, line 62-63: This is not quite right. It is equation 1 that delivers the seasonal pattern by itself (prices are higher in non-harvest months because supply is coming from storage from the previous harvest). Equation 2 is just a reduced-form representation of the implications of equation 1. Equation 2 would make more sense if you present this more clearly as a 2-period model (harvest vs. non-harvest) rather than monthly. Prices are higher in the non-harvest period because of storage costs. Second, line 81-83: It was not clear what you meant by “domestic harvest enters weakly” as the domestic harvest does not appear in equation 5. Either include it explicitly in equation 5 or don’t mention it in the sentence. Also, why does equation 5 hold approximately and not with equality? It might also help to include another equation here after equation 5 that would be analogous to equation 4 but for the imported variety case. 1) The map is helpful but leaves me wondering two things. Why do some markets appear to have no links? And why are there no markets in Lagos and vicinity? It would be helpful to clarify in the text. Perhaps add more about the snowball approach or how the starting markets were selected. 2) This comment has been addressed. 3) This comment has been addressed. 4) This comment has been addressed. 5) This comment has been addressed. 6) This comment has been addressed. Reviewer #2: In the first review report, some concerns were raised. These concerns were successfully addressed by the authors in the revised manuscript. The manuscript can be accepted in the present form. ****** 7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files. If you choose “no”, your identity will remain anonymous but your review may still be made public. Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy. Reviewer #1: No Reviewer #2: Yes: Cristian Valeriu Stanciu ******** [NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.] To ensure your figures meet our technical requirements, please review our figure guidelines: https://journals.plos.org/plosone/s/figures You may also use PLOS’s free figure tool, NAAS, to help you prepare publication quality figures: https://journals.plos.org/plosone/s/figures#loc-tools-for-figure-preparation. NAAS will assess whether your figures meet our technical requirements by comparing each figure against our figure specifications. https://doi.org/10.1371/journal.pone.0339577.r003
Revision 2
25 Nov 2025 Author Response Reviewer 1: Thank you for addressing my comments. I have some last minor points (numbers refer to my numbered comments on the previous version): Reviewer Comment 0: The new section on the Theoretical Framework is helpful. However, there are two points of confusion. First, line 62-63: This is not quite right. It is equation 1 that delivers the seasonal pattern by itself (prices are higher in non-harvest months because supply is coming from storage from the previous harvest). Equation 2 is just a reduced-form representation of the implications of equation 1. Equation 2 would make more sense if you present this more clearly as a 2-period model (harvest vs. non-harvest) rather than monthly. Prices are higher in the non-harvest period because of storage costs. Second, line 81-83: It was not clear what you meant by “domestic harvest enters weakly” as the domestic harvest does not appear in equation 5. Either include it explicitly in equation 5 or don’t mention it in the sentence. Also, why does equation 5 hold approximately and not with equality? It might also help to include another equation here after equation 5 that would be analogous to equation 4 but for the imported variety case. Response to Reviewer Comment 0: We are thankful for this hint from the reviewer. We have now revised the theoretical framework accordingly. First, we now make it explicit that the storage no-arbitrage condition alone generates the seasonal pattern. To do so, we introduce a simple two-period example (harvest vs. non-harvest) and explain that prices are higher in the non-harvest period because supply comes from stored stocks and must cover storage costs. Second, in the subsection on imported varieties, we removed the phrase “domestic harvest enters weakly” since harvest does not appear in that equation, and we now write the imported price relationship with equality rather than approximately. As you suggested, we also add a brief expression for the cross-market price gap for imports, directly analogous to the domestic-gap case. These changes address the points you raised. The updates can be found in line 64-76 and line 92-99. Reviewer Comment 1: The map is helpful but leaves me wondering two things. Why do some markets appear to have no links? And why are there no markets in Lagos and vicinity? It would be helpful to clarify in the text. Perhaps add more about the snowball approach or how the starting markets were selected. Response to Reviewer Comment 1: We are thankful for the guidance from the reviewer. We should start by admitting that Lagos was excluded largely because our limited budget could not cover it. Our snowball approach started from the largest known grain markets in the key production areas – predominantly in Northern Nigeria. These include Dawanau near Kano and Mutum Biu in Taraba State. Given our extensive coverage of Bodija market in Ibadan (about 70 miles from Lagos), and past research that shows the significance of Bodija to price movements in the southwest of Nigeria, we focused on the 97 markets used for this paper, with a reasonable level of confidence that our main findings, if we had the budget to include Lagos, would not be significantly different from our main findings as they are. We are thankful that the reviewer used the phrase “appear to” in the question. We selected key link-markets that connect farms to consumers for our price surveys, but a few of these were not linked to other key markets – largely being linked to local food grain markets that are more than two steps removed from other key grain markets. Given that we could not track prices in all markets that we visited in 2022 - roughly 300 of them, there was no reason to plot a network graph that includes markets for which we have no price data. Furthermore, a network graph with 97 nodes is more legible and instructive than one with three times that number. In sum, the network graph reflects only linkages between key markets, specifically, the 97 markets for which we track prices. We have now updated the paper to explain that we exclude Lagos because of budget limits, and why a few nodes in the graph appear to have no connections, because they had no reported links to other key grain markets that we track in our data. The updates can be found near line 177-190 of the revised paper. Attachments Attachment Submitted filename: PlosOneRound2Revs1.docx https://doi.org/10.1371/journal.pone.0339577.r004
10 Dec 2025 Decision Letter - Eugenio Sebastian Antonio Bobenrieth, Editor Price Convergence in Grain Markets with Seasonal Differences PONE-D-25-30518R2 Dear Dr. Olabisi, We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements. Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication. An invoice will be generated when your article is formally accepted. Please note, if your institution has a publishing partnership with PLOS and your article meets the relevant criteria, all or part of your publication costs will be covered. Please make sure your user information is up-to-date by logging into Editorial Manager at Editorial Manager® and clicking the ‘Update My Information' link at the top of the page. For questions related to billing, please contact billing support. If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org. Kind regards, Eugenio Bobenrieth Academic Editor PLOS One Additional Editor Comments (optional): Reviewers' comments: https://doi.org/10.1371/journal.pone.0339577.r005
Formally Accepted
Acceptance Letter - Eugenio Sebastian Antonio Bobenrieth, Editor PONE-D-25-30518R2 PLOS One Dear Dr. Olabisi, I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS One. Congratulations! Your manuscript is now being handed over to our production team. At this stage, our production department will prepare your paper for publication. This includes ensuring the following: * All references, tables, and figures are properly cited * All relevant supporting information is included in the manuscript submission, * There are no issues that prevent the paper from being properly typeset You will receive further instructions from the production team, including instructions on how to review your proof when it is ready. Please keep in mind that we are working through a large volume of accepted articles, so please give us a few days to review your paper and let you know the next and final steps. Lastly, if your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org. You will receive an invoice from PLOS for your publication fee after your manuscript has reached the completed accept phase. If you receive an email requesting payment before acceptance or for any other service, this may be a phishing scheme. Learn how to identify phishing emails and protect your accounts at https://explore.plos.org/phishing. If we can help with anything else, please email us at customercare@plos.org. Thank you for submitting your work to PLOS ONE and supporting open access. Kind regards, PLOS ONE Editorial Office Staff on behalf of Dr. Eugenio Sebastian Antonio Bobenrieth Academic Editor PLOS One https://doi.org/10.1371/journal.pone.0339577.r006

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