# How to Communicate Feasibility Limits to Reviewers ## Quick Answer - Explain feasibility limits with specific evidence about equipment, samples, or ethics instead of general statements about difficulty. - Pair each limitation with a concrete alternative that still answers the reviewer's underlying scientific question. - Acknowledge reviewer concerns directly and document your reasoning so editors can verify the decision independently. ## Understanding Reviewer Feasibility Concerns Peer reviewers request additional experiments for many reasons. Some requests address genuine gaps in the evidence. Others reflect uncertainty about whether the authors considered a particular approach. When a requested experiment is not feasible, the response letter must show that the authors understood the request, evaluated it seriously, and had concrete reasons for declining. The Committee on Publication Ethics Core Practices describe peer review as a process where journals rely on reviewers to assess the validity and significance of submitted work. Reviewers are expected to provide constructive comments that help authors improve their manuscripts. When authors respond to those comments, the exchange should remain professional and evidence based. The goal is not to win an argument but to demonstrate that the final published version represents the strongest possible presentation of the work within real constraints. Feasibility problems fall into several categories. Equipment may not be available at the authors' institution. The biological samples may have been consumed during the original experiments. The requested method may require more animals than an ethics committee would approve. The timeline may extend beyond the funding period. The cost may exceed the project budget. The technique may require expertise that no member of the research team possesses. Each category requires a different response strategy. The response letter is a formal document that becomes part of the peer review record. Journals may share the response letter with reviewers, and some journals publish the review history alongside the accepted manuscript. The tone and content of the response therefore matter beyond the immediate decision. A well reasoned response demonstrates that the authors understand the scientific method and can make defensible judgments about research design. ## Core Principles for Responding to Feasibility Requests ### Separate Feasibility from Desirability A reviewer may request an experiment that would improve the study if it were possible. The response should acknowledge the scientific value of the suggestion before explaining why it cannot be implemented. This distinction matters because it shows the reviewer that the authors are not dismissing the comment out of hand. For example, a reviewer might request a longitudinal follow-up of animal subjects to assess long term outcomes. The authors may agree that long term data would strengthen the conclusions. The response can state that agreement explicitly, then explain that the funding period ended and the animals were rehomed according to the institutional protocol. The reviewer sees that the authors share the scientific goal but face a resource constraint. The response should never imply that the reviewer's suggestion was unreasonable. Even when a request seems disconnected from the study design, the authors should assume good faith and respond with respect. The Committee on Publication Ethics Core Practices emphasize that peer review should be conducted fairly and that all participants should treat each other with respect. ### Distinguish Absolute from Relative Barriers Some feasibility barriers are absolute. The equipment does not exist at the institution. The samples were destroyed during analysis. The species is protected and cannot be collected. The ethics committee has already denied the protocol. These barriers cannot be overcome by effort or creativity. Other barriers are relative. The experiment could be done but would require additional funding, a longer timeline, or collaboration with another institution. These barriers may be negotiable, but the authors must decide whether the negotiation is worth the delay and cost. The response letter should be clear about which type of barrier applies. If the barrier is absolute, the authors should say so directly and provide evidence. If the barrier is relative, the authors should explain what would be required to overcome it and why that investment is not justified for the current manuscript. ### Provide Evidence for Every Claim A response that says the equipment is unavailable is weaker than a response that says the institution's core facility inventory does not include the required instrument and that the nearest available instrument is at a facility 400 miles away. The second version gives the reviewer something concrete to evaluate. Evidence can take many forms. Institutional records showing equipment purchases. Correspondence with the ethics committee showing the denial. Sample inventory logs showing depletion. Budget documents showing the funding period. Vendor quotes showing the cost of the required reagent. The response letter should cite the relevant evidence and offer to provide documentation if the editor requests it. The National Library of Medicine Research Methods Resources provide access to authoritative biomedical books and research method references that can help authors describe their methods accurately. When a feasibility limitation relates to a specific method, citing the methodological literature can strengthen the response. ## At a Glance | Feasibility Barrier | Evidence to Provide | Response Strategy | | --- | --- | --- | | Equipment not available | Institutional instrument inventory, vendor quotes, facility access records | State the specific instrument gap and describe the closest available alternative | | Samples depleted | Sample tracking logs, remaining quantity records, storage documentation | Confirm the sample count and explain why additional analysis is impossible | | Ethics restrictions | Ethics committee approval letter, protocol amendment history | Quote the relevant restriction and describe the approved protocol | | Funding or timeline limits | Grant award documents, project timeline, budget records | Explain the funding period and offer a partial or future alternative | | Expertise gap | Laboratory training records, personnel qualifications | Acknowledge the gap and describe the collaborative option | | Animal welfare constraints | Institutional animal care and use committee records | Describe the welfare standard and the approved animal numbers | ## Practical Response Workflow ### Step 1: Inventory the Reviewer Requests Before writing any response, list every reviewer comment that requests additional work. Some comments will be direct requests for new experiments. Others will be phrased as questions that imply an experiment should have been done. Still others will be suggestions that the authors may choose to accept or decline. Create a table with columns for the reviewer comment, the requested experiment, the feasibility barrier, and the proposed response. This table will help organize the response letter and ensure that no comment is overlooked. ### Step 2: Assess Feasibility for Each Request For each requested experiment, determine whether it is feasible within the current study constraints. Consider the following factors: - Equipment availability at the institution - Sample availability and remaining quantity - Ethics approval status and the possibility of amendment - Funding period and remaining budget - Timeline to the journal's revision deadline - Expertise within the research team - Animal or human subject availability - Regulatory or legal restrictions Record the assessment for each factor. If any factor makes the experiment impossible, document the evidence. ### Step 3: Draft the Response for Each Request For each request, write a response that includes the following elements: 1. A direct acknowledgment of the reviewer's request 2. An explanation of the feasibility barrier 3. Evidence supporting the barrier 4. An alternative that addresses the reviewer's underlying concern 5. A statement of what the authors have done in the revision The alternative is important. Reviewers request experiments because they want to see evidence that addresses a specific concern. If the authors cannot provide that exact evidence, they should provide the closest possible alternative. This might be a supplementary analysis, a sensitivity analysis, a discussion of the limitation, or a citation to published work that addresses the concern. ### Step 4: Draft the Response Letter The response letter should be organized by reviewer comment. Each comment should be quoted or paraphrased, followed by the response. The letter should be written in a professional tone and should avoid defensive language. The Committee on Publication Ethics Core Practices describe the responsibilities of authors in the peer review process. Authors are expected to respond to reviewer comments in a timely and professional manner. The response letter should demonstrate that the authors have taken the review seriously and have made a good faith effort to address the concerns. ### Step 5: Verify the Evidence Before submitting the response, verify that every evidence claim is accurate. Check the equipment inventory. Confirm the sample count. Review the ethics approval. Confirm the funding period. The response letter should not contain any claim that cannot be verified. ## Diplomatic Language for Feasibility Responses The language used in the response letter shapes how the reviewer perceives the authors' attitude. A response that sounds dismissive or defensive can create a negative impression even when the scientific argument is sound. A response that sounds respectful and constructive can preserve a positive relationship with the reviewer. ### Acknowledging the Request Begin each response by acknowledging the reviewer's request in specific terms. This shows that the authors read the comment carefully and understood the intent. - "We thank the reviewer for this suggestion. We agree that long term follow up would provide valuable information about the durability of the observed effect." - "The reviewer raises an important point about the potential for confounding by seasonal variation. We have considered this possibility in our analysis." - "We appreciate the reviewer's suggestion to include a positive control group. This is a reasonable request that we have addressed as follows." ### Explaining the Barrier After acknowledging the request, explain the feasibility barrier in clear and specific terms. Avoid vague language such as "not possible" or "cannot be done." Instead, describe the specific constraint. - "The instrument required for this analysis is not available at our institution. Our instrument facility maintains an inventory of available equipment, and the required instrument is not listed. The nearest facility with this instrument is located at a university in another state." - "The samples used in this study were fully consumed during the initial analysis. The sample tracking log shows that the remaining quantity was zero after the final measurement." - "The ethics committee approval for this study specifies a maximum of 40 animals per group. The requested experiment would require 60 animals per group to achieve adequate statistical power, which exceeds the approved limit." ### Offering an Alternative After explaining the barrier, offer an alternative that addresses the reviewer's underlying concern. The alternative should be concrete and feasible. - "To address the reviewer's concern about long term outcomes, we have added a discussion of the published literature on the durability of this intervention in similar populations." - "To address the concern about seasonal variation, we have added a sensitivity analysis that adjusts for the month of enrollment." - "To address the concern about the positive control, we have cited a published study that used the same positive control in a similar population." ### Closing the Response Close each response with a statement that the authors have considered the request and have made the best possible decision within the constraints. This statement should be respectful and should not invite further debate. - "We believe this approach addresses the reviewer's concern within the constraints of the available resources." - "We hope this explanation clarifies the feasibility limitations and the alternative we have provided." - "We are grateful for the reviewer's careful consideration of our work and for the opportunity to respond." ## Common Feasibility Scenarios ### Lack of Equipment Equipment availability is a common feasibility barrier. The response should describe the specific equipment gap and the institutional context. The response should also describe any alternative equipment that was considered and why it was not suitable. For example, a reviewer might request a specific imaging modality that the institution does not have. The response could state that the institution's imaging facility does not have the requested modality, that the nearest facility is at a different institution, and that the cost of outsourcing the analysis would exceed the project budget. The response could then offer an alternative analysis that uses the available imaging data. ### Sample Depletion Sample depletion is another common barrier. The response should describe the sample tracking process and the remaining quantity. The response should also describe the alternative analysis that was performed or the discussion that was added. For example, a reviewer might request a genetic analysis that requires a specific tissue sample. The response could state that the tissue samples were fully consumed during the initial analysis, that the sample tracking log confirms the depletion, and that the authors have added a discussion of the genetic analysis in the published literature. ### Ethical Restrictions Ethical restrictions are a barrier that requires careful explanation. The response should describe the ethics approval process and the specific restrictions in the approval. The response should also describe the alternative that was used. For example, a reviewer might request a larger sample size to improve statistical power. The response could state that the ethics committee approved a maximum of 40 animals per group, that the approval was based on the principle of reducing the number of animals used, and that the authors have added a discussion of the statistical power and the limitations of the sample size. ### Time and Funding Limits Time and funding limits are often the most difficult barriers to explain because they are not scientific limitations. The response should describe the funding period and the timeline of the project. The response should also describe the alternative that was performed within the available time and budget. For example, a reviewer might request a follow-up study that would require an additional year of data collection. The response could state that the funding period ended before the follow-up could be completed, that the project timeline was established at the start of the grant, and that the authors have added a discussion of the follow-up in the published literature. ### Expertise Gaps Expertise gaps are a barrier that can be addressed through collaboration. The response should describe the expertise that is missing and the collaboration that was considered. The response should also describe the alternative that was used. For example, a reviewer might request a bioinformatics analysis that the research team does not have the expertise to perform. The response could state that the team does not have a bioinformatician, that the team considered collaborating with a bioinformatics core facility, and that the core facility was not available within the project timeline. The response could then describe the alternative analysis that was performed. ## Records and Measurements The response letter should be supported by records that can be verified. The following records are useful for feasibility responses: - Equipment inventory records from the institution - Sample tracking logs showing the remaining quantity - Ethics committee approval documents and correspondence - Grant award documents and budget records - Project timeline and milestone records - Training records for the research team - Vendor quotes for equipment or services These records should be maintained in the project file and should be available if the editor requests documentation. The response letter should cite the records and offer to provide them. ## Common Failure Patterns ### Defensive Language A response that sounds defensive can create a negative impression. Phrases such as "the reviewer misunderstands" or "the reviewer is wrong" should be avoided. Instead, the response should acknowledge the reviewer's perspective and explain the authors' reasoning. ### Vague Explanations A response that says "this is not feasible" without explaining why is not persuasive. The response should describe the specific barrier and provide evidence. ### Ignoring the Underlying Concern A response that declines the request without offering an alternative does not address the reviewer's underlying concern. The response should always offer an alternative that addresses the concern. ### Overpromising A response that promises to do something that is not feasible creates a problem for the revision. The response should only promise what can be delivered. ### Inconsistent Evidence A response that cites evidence that is not consistent with the manuscript may create a credibility problem. The response should be consistent with the manuscript and the project records. ## Welfare and Safety Context When the feasibility barrier involves animal or human subjects, the response should describe the welfare and safety considerations that led to the restriction. The response should not imply that the restriction was arbitrary. Instead, the response should describe the ethical framework that guided the decision. The National Institutes of Health Grants and Funding pages describe the expectations for research involving animal and human subjects. The response should be consistent with these expectations and should describe the institutional approval process. ## Professional Escalation Criteria If the editor or the reviewer continues to request an experiment that is not feasible, the authors may need to escalate the issue. The escalation should be directed to the editor, not the reviewer. The authors should explain the feasibility barrier and provide the evidence. The editor may decide to accept the response or may request additional information. The Committee on Publication Ethics Core Practices describe the responsibilities of editors in the peer review process. Editors are responsible for making decisions about the manuscript and for resolving disputes between authors and reviewers. If the authors believe that the reviewer's request is unreasonable, they should raise the issue with the editor. ## Frequently Asked Questions ### How should I respond to a reviewer who requests an experiment that requires equipment my institution does not have? Describe the specific equipment gap and the institution's inventory records. State that the nearest facility is located elsewhere and that the cost of outsourcing would exceed the project budget. Offer an alternative analysis that uses the available equipment. ### What should I do if the reviewer requests a larger sample size than the ethics committee approved? Describe the ethics approval process and the specific restriction in the approval. State that the approval was based on the principle of reducing the number of animals used. Offer an alternative that addresses the reviewer's concern about statistical power, such as a sensitivity analysis or a discussion of the published literature. ### How do I explain that the samples were fully consumed during the initial analysis? Describe the sample tracking process and the remaining quantity. State that the sample tracking log shows that the final sample was zero. Offer an alternative analysis that uses the available data or a discussion of the published literature. ### What if the reviewer requests a follow-up study that requires additional funding? Describe the funding period and the project timeline. State that the funding period ended before the follow-up could have been conducted. Offer an alternative that addresses the reviewer's concern, such as a discussion of the published literature on the durability of the intervention. ### How should I respond to a reviewer who requests a technique that my team does not have the expertise to perform? Describe the expertise gap and the collaboration that was considered. State that the collaboration was not available within the project timeline. Offer an alternative analysis that uses the available expertise. ### What if the reviewer requests an experiment that is scientifically valuable but not feasible? Acknowledge the scientific value of the request. Explain the feasibility barrier and provide evidence. Offer an alternative that addresses the reviewer's underlying concern. The response should show that the authors understood the request and made a reasonable decision. ### How do I respond to a reviewer who is not satisfied with my feasibility explanation? If the reviewer is not satisfied, the response should be directed to the editor. Explain the feasibility barrier and provide the evidence. The editor should decide whether the request is reasonable and whether the response is acceptable. ### Should I ever agree to do an experiment that is not feasible? No. The response should not promise to do something that is not feasible. The response should explain the barrier and offer an alternative. If the editor insists on the experiment, the authors should explain the barrier again and provide the evidence. ## Using the Evidence | Source | Best use in this topic | Important limitation | |---|---|---| | [Research Methods Resources](https://www.ncbi.nlm.nih.gov/books) | official guidance | Check the linked page for current local requirements | | [EQUATOR Network](https://www.equator-network.org/) | official guidance | Check the linked page for current local requirements | | [Core Practices](https://publicationethics.org/core-practices) | official guidance | Check the linked page for current local requirements | ## Related Articles - [Randomized Experiments: Why Randomization Matters](/blog/guides/randomized-experiments-why-randomization-matters) - [The Role of the Research Ethics Committee: What Researchers Need to Know](/blog/guides/the-role-of-the-research-ethics-committee-what-researchers-need-to-know) - [Why Environmental Science Is an Interdisciplinary Field: A Practical Guide](/blog/careers/why-environmental-science-is-an-interdisciplinary-field-a-practical-guide) - [Controlled Experiments: What They Are and Why They Matter](/blog/guides/controlled-experiments-what-they-are-and-why-they-matter) - [Open Access Practices for Researchers: A Guide](/blog/guides/open-access-practices-for-researchers-a-guide) ## References and Further Reading - [Research Methods Resources](https://www.ncbi.nlm.nih.gov/books). National Library of Medicine. - [EQUATOR Network](https://www.equator-network.org/). EQUATOR Network. - [Core Practices](https://publicationethics.org/core-practices). Committee on Publication Ethics. - [NIH Grants and Funding](https://grants.nih.gov/). National Institutes of Health. - [ORCID for Researchers](https://info.orcid.org/researchers). ORCID. - [Data Management and Sharing Policy](https://sharing.nih.gov/data-management-and-sharing-policy). National Institutes of Health. - [NCBI Literature Resources](https://www.ncbi.nlm.nih.gov/). National Center for Biotechnology Information. - [PubMed](https://pubmed.ncbi.nlm.nih.gov/). National Library of Medicine. > This article is educational and does not replace institutional policy, professional advice, or applicable safety and regulatory requirements.