# When a Reviewer Asks for New Experiments You Can't Do ## Quick Answer - When a reviewer requests experiments you cannot perform, evaluate feasibility across resources, time, and technical capacity before responding. - Draft a structured response that explains constraints honestly and proposes alternative evidence that addresses the underlying concern. - Peer review expectations vary by journal and field, so consult publication ethics guidance and reporting standards before finalizing your reply. ## Understanding the Reviewer Request Peer review exists to improve manuscripts through independent critique. Reviewers ask for additional experiments for many reasons. Some requests target genuine gaps in evidence. Others reflect a reviewer's preferred methodology or a misunderstanding of your study design. Your first task is to determine what the reviewer actually needs to see before you decide what you can provide. The [Committee on Publication Ethics Core Practices](https://publicationethics.org/core-practices) describe peer review as a process that should help authors strengthen their work. The same guidance emphasizes that journals should have clear policies about how reviewers and editors handle disputes. When you receive a request you cannot fulfill, you are not refusing to engage with peer review. You are participating in a negotiation about what evidence is necessary and what is feasible. Read the reviewer comment several times before drafting any response. Identify the specific concern underneath the requested experiment. A request for a longer animal trial may reflect worry about chronic toxicity. A request for a different cell line may reflect concern about generalizability. A request for mechanistic data may reflect uncertainty about your interpretation. When you understand the underlying question, you can propose alternative approaches that answer it. ## Feasibility Assessment Framework Before you write anything, assess whether the requested experiment is truly impossible or merely difficult. Use a structured evaluation that separates resource constraints, time constraints, and technical constraints. This assessment becomes the backbone of your response letter. ### Resource Constraints Resource constraints include funding, equipment, materials, and personnel. Calculate what the experiment would cost in direct expenses and staff time. Consider whether your current grant can absorb the cost or whether you would need additional funding. The [NIH Grants and Funding portal](https://grants.nih.gov/) describes how research budgets are planned and justified at the application stage. If your project budget did not include the requested work, you may not have authority to spend funds on it without amending your plan. Laboratory resources matter as much as money. A requested experiment may require equipment you do not have access to. It may require reagents that are no longer manufactured. It may require animal models that are not available in your institution. Document these limitations specifically. A vague statement that you lack resources is less persuasive than a precise explanation that the required antibody is discontinued or the animal facility cannot house the requested strain. ### Time Constraints Time constraints include project deadlines, funding end dates, and the practical duration of the experiment itself. Some experiments take months or years to complete. A longitudinal animal study cannot be compressed. A breeding program to generate a specific genotype follows its own calendar. If your funding ends before the experiment could finish, you face a hard deadline that no amount of effort can change. Consider also the opportunity cost of time. Every week spent on a requested experiment is a week not spent on other work. If the requested experiment would delay your manuscript by a year, the cost may exceed the benefit. The [NIH Data Management and Sharing Policy](https://sharing.nih.gov/data-management-and-sharing-policy) emphasizes planning research activities in advance. Your original plan represented your best judgment about what was feasible. A reviewer request that would require abandoning that plan deserves careful scrutiny. ### Technical Constraints Technical constraints include expertise, methodology, and feasibility of the experiment itself. Some experiments are technically impossible with current methods. Others require specialized expertise your team does not have. Still others would produce data that cannot be interpreted because the experimental system does not support the approach. Be honest about technical limitations. If you do not know how to perform a technique, say so directly. If the technique requires a collaborator you cannot find, explain that. If the experiment would require a sample size that is biologically impossible to collect, show the calculation. Reviewers respond better to specific technical explanations than to general claims of impossibility. ## Building Your Response Strategy Once you have assessed feasibility, decide how to respond. You have several options. You can perform the experiment if it is feasible. You can propose an alternative experiment that answers the same question. You can explain why the experiment is unnecessary. You can provide existing data that already addresses the concern. You can combine these approaches. ### Option One: Perform the Experiment If the experiment is feasible within your resources and timeline, consider doing it. Some reviewer requests improve manuscripts meaningfully. A requested control experiment may strengthen your conclusions. A requested replication may increase confidence in your findings. Weigh the cost against the benefit before declining. When you perform the experiment, report the results honestly even if they do not support your original interpretation. The [EQUATOR Network](https://www.equator-network.org/) provides reporting guidelines that help authors present methods and results transparently. Following these guidelines when you add new experiments keeps your reporting consistent with your original manuscript. ### Option Two: Propose an Alternative An alternative experiment can address the reviewer's underlying concern without replicating the exact request. If the reviewer wants a longer time course, propose additional time points within your existing experiment. If the reviewer wants a different animal model, propose a complementary in vitro approach. If the reviewer wants mechanistic data, propose a targeted experiment that tests your proposed mechanism directly. Frame alternatives as solutions to the reviewer's concern, not as substitutes for their request. Explain how the alternative answers the same question. Show that you have thought carefully about what the reviewer needs to see. A well-designed alternative often satisfies reviewers more than a partial attempt at the original request. ### Option Three: Explain Why the Experiment Is Unnecessary Some reviewer requests are not necessary for the manuscript to be sound. The requested experiment may test a hypothesis you never made. It may address a question outside the scope of your study. It may duplicate data already in the manuscript. It may require a study design that would introduce new confounders. Explain why the experiment is unnecessary with specific reasoning. Reference the data you already present. Show how the existing evidence answers the reviewer's concern. If the reviewer misunderstood your methods, clarify the misunderstanding. If the reviewer missed a control you already included, point to it directly. ### Option Four: Provide Existing Data You may already have data that addresses the reviewer's concern. This data may be in the manuscript, in supplementary materials, or in your laboratory records. Review the data you have before drafting your response. You may find that a requested experiment was already performed as part of your original study. When you provide existing data, present it clearly. Explain where the data appears in the manuscript or supplementary materials. If the data is not currently in the manuscript, offer to add it. The [Research Methods Resources collection from the National Library of Medicine](https://www.ncbi.nlm.nih.gov/books) includes guidance on presenting research methods and results clearly. Use this guidance to decide how to present existing data in your response. ## Structuring Your Response Letter A response letter is a formal document that accompanies your revised manuscript. It should be organized, specific, and respectful. Reviewers read response letters to understand what you changed and why. A well-structured letter makes their job easier and increases the chance of acceptance. ### Response Letter Format Organize your response letter by reviewer comment. Number each comment and respond to it individually. For each comment, include the reviewer's original text, your response, and a description of what you changed in the manuscript. This format lets the reviewer verify that you addressed each concern. Begin your letter with a brief summary of the major changes you made. This summary helps the editor and reviewer understand the scope of your revision. Keep the summary concise. The detailed responses follow. ### Tone and Language Maintain a respectful tone throughout your response letter. Do not argue with the reviewer or dismiss their concerns. Acknowledge the value of their feedback even when you disagree. Explain your reasoning clearly and without defensiveness. Use precise language when describing your constraints. Instead of saying the experiment is impossible, say that it would require resources beyond your current capacity. Instead of saying the experiment is unnecessary, say that the existing data already addresses the concern. Precise language keeps the conversation focused on evidence instead of emotion. ### What to Include in Each Response For each reviewer comment, include the following elements. First, restate the reviewer's concern in your own words to show you understood it. Second, explain your assessment of the request, including feasibility considerations. Third, describe what you did in response, whether that is performing the experiment, proposing an alternative, or explaining why the request cannot be met. Fourth, state where the change appears in the revised manuscript. ## Handling Different Types of Requests Reviewer requests fall into recognizable patterns. Recognizing the pattern helps you respond efficiently and effectively. ### Requests for Larger Sample Sizes Reviewers often ask for larger sample sizes to increase statistical power. This request may be reasonable if your sample size is genuinely too small. It may be unreasonable if your sample size is appropriate for your study design or if larger samples are not feasible. If you cannot increase your sample size, explain why. You may have reached the maximum number of animals your ethics approval allows. You may have collected samples over a fixed recruitment period that has ended. You may have analyzed all available clinical specimens. Provide the specific constraint and explain how your current sample size supports your conclusions. ### Requests for Additional Time Points Time course experiments require planning and resources. A reviewer may ask for additional time points to better characterize a response over time. If you cannot add time points, explain that your experimental design was fixed at the start of the study. Offer alternative evidence that characterizes the temporal response, such as data from your existing time points or published literature. ### Requests for Mechanistic Studies Mechanistic studies can be extensive and expensive. A reviewer may ask for experiments that identify the molecular mechanism underlying your observations. If you cannot perform these experiments, explain that your study was designed to characterize a phenomenon instead of establish a mechanism. Offer what evidence you have about the mechanism and suggest the mechanistic question as a direction for future work. ### Requests for Different Model Systems Reviewers may ask you to repeat your study in a different animal model, cell line, or patient population. This request may be reasonable if your findings are likely to be model-specific. It may be unreasonable if the requested model is not relevant to your question or is not available to you. Explain why your chosen model is appropriate for your question. If the requested model is not available, say so specifically. Offer evidence from the literature that supports the generalizability of your findings. ### Requests for Replication Replication requests ask you to repeat experiments to confirm your results. If you have already replicated your key findings, point to that data. If you have not, explain whether replication is feasible. Some experiments are inherently difficult to replicate because they use unique samples or specialized systems. ## The Role of Reporting Guidelines Reporting guidelines help authors present their research completely and transparently. When you revise a manuscript, consulting the appropriate reporting guideline can help you respond to reviewer requests. The [EQUATOR Network](https://www.equator-network.org/) maintains a comprehensive database of reporting guidelines for different study types. These guidelines tell you what information reviewers and readers expect to see. If a reviewer asks for information that a reporting guideline says should be included, you should provide it. If a reviewer asks for information that is not required by the relevant guideline, you have a stronger basis for explaining why the request is unnecessary. Reporting guidelines give you a neutral reference point for discussions about what a manuscript should contain. ## Publication Ethics Considerations Publication ethics govern how authors, reviewers, and editors behave. Understanding these ethics helps you respond to reviewer requests appropriately. The [Committee on Publication Ethics Core Practices](https://publicationethics.org/core-practices) describe expectations for peer review, data access, and authorship. ### Peer Review Expectations Peer review should be fair and constructive. Reviewers should provide feedback that helps authors improve their work. Authors should respond to reviewer feedback seriously and respectfully. When you cannot perform a requested experiment, you are not violating peer review expectations. You are engaging in the normal process of negotiation that peer review involves. ### Data Access and Sharing Some reviewer requests relate to data access. A reviewer may ask to see raw data or to have data deposited in a repository. The [NIH Data Management and Sharing Policy](https://sharing.nih.gov/data-management-and-sharing-policy) describes expectations for data sharing in NIH-funded research. If your funding requires data sharing, you should comply with those requirements. If your funding does not require data sharing, you may still choose to share data to address reviewer concerns. ### Authorship and Contributions Reviewer requests should not change authorship. If a reviewer suggests that a collaborator with specific expertise should be added as an author, consider whether that person made a substantial contribution to the work. The [Committee on Publication Ethics Core Practices](https://publicationethics.org/core-practices) describe authorship criteria that require substantial contributions to conception, design, data acquisition, analysis, or interpretation. Adding an author solely to satisfy a reviewer is not appropriate. ## When to Escalate to the Editor Most reviewer requests can be resolved through direct response. Some situations require escalation to the editor. Escalate when the request is unreasonable, when the reviewer is not engaging with your responses, or when you believe the review process is unfair. ### Unreasonable Requests A request may be unreasonable if it is impossible, unethical, or outside the scope of the study. If a reviewer asks you to perform an experiment that would violate animal welfare standards or human subjects protections, you should decline and explain why. If a reviewer asks for data that cannot exist, you should explain that clearly. ### Reviewer Non-Engagement If you respond to a reviewer's comments and the reviewer repeats the same request without acknowledging your response, you may need to involve the editor. Explain to the editor that you have addressed the concern and that the reviewer has not engaged with your response. The editor can mediate the discussion. ### Unfair Review If you believe the review process is unfair, contact the editor. Examples of unfair review include personal attacks, requests for citations to the reviewer's own work without justification, and demands for experiments that are clearly impossible. The [Committee on Publication Ethics Core Practices](https://publicationethics.org/core-practices) describe expectations for fair peer review. Editors have responsibility to ensure that review is conducted fairly. ## Practical Steps for Drafting Your Response Follow these steps when drafting your response to a reviewer who requests experiments you cannot perform. ### Step One: List All Reviewer Comments Create a numbered list of every reviewer comment. Include comments from all reviewers and the editor. This list becomes the outline for your response letter. ### Step Two: Classify Each Comment For each comment, determine whether you can perform the requested experiment, propose an alternative, or explain why the request cannot be met. This classification helps you plan your revision work. ### Step Three: Assess Feasibility For each request you cannot immediately fulfill, complete the feasibility assessment. Document the resource, time, and technical constraints. This documentation supports your response. ### Step Four: Draft Responses Draft a response for each comment. Include the reviewer's original text, your response, and a description of manuscript changes. Keep responses specific and evidence-based. ### Step Five: Review and Revise Review your draft response letter for tone and clarity. Ask a colleague to read it and provide feedback. Revise as needed before submitting. ## At a Glance | Request Type | Feasibility Question | Response Strategy | | --- | --- | --- | | Larger sample size | Can additional samples be collected within ethics approval and funding? | Perform if feasible, otherwise explain sample availability limits and statistical justification | | Additional time points | Can the experimental timeline be extended without exceeding funding or facility limits? | Perform if feasible, otherwise provide existing time course data and literature support | | Mechanistic studies | Does your team have the technical expertise and resources for the requested approach? | Propose a targeted alternative experiment or explain scope limitations | | Different model system | Is the requested model available and relevant to your research question? | Explain model choice rationale or provide generalizability evidence from literature | | Replication | Have you already replicated key findings in your existing data? | Point to existing replication data or explain replication feasibility | ## Common Failure Patterns Authors often make predictable mistakes when responding to reviewer requests they cannot fulfill. Recognizing these patterns helps you avoid them. ### Vague Refusals A vague refusal says the experiment is not possible without explaining why. This response frustrates reviewers because it gives them nothing to evaluate. Replace vague refusals with specific explanations of resource, time, or technical constraints. ### Defensive Tone A defensive response argues with the reviewer instead of addressing the concern. This tone damages your credibility and makes acceptance less likely. Maintain a respectful tone even when you disagree with the reviewer. ### Ignoring the Underlying Concern Responding only to the surface request without addressing the underlying concern often leads to repeated requests. If the reviewer wants to know whether your findings generalize, explaining that you cannot use a different model does not answer the question. Propose alternative evidence that addresses generalizability. ### Overpromising Promising experiments you cannot deliver creates problems later. If you say you will perform an experiment and then cannot, you lose credibility with the editor and reviewer. Only commit to what you can actually do. ### Incomplete Documentation Failing to document your feasibility assessment weakens your response. Reviewers want to see that you have thought carefully about their request. Include specific details about why the experiment cannot be performed. ## Records and Documentation Keep records of your response process. These records help you if the manuscript goes through multiple rounds of review. They also help you if you need to escalate a dispute to the editor. ### What to Document Document the reviewer comments, your feasibility assessments, your responses, and any correspondence with the editor. Keep copies of all versions of your response letter and revised manuscript. This documentation creates a complete record of the revision process. ### Using ORCID for Research Records The [ORCID for Researchers page](https://info.orcid.org/researchers) describes how researchers can maintain a persistent identifier that links to their publications and activities. Keeping your ORCID record current helps you track your manuscripts through the review process. It also provides a stable record of your research contributions. ## Limitations of This Approach This framework has limitations. It cannot guarantee that a reviewer will accept your response. Some reviewers will not be satisfied with any explanation. Some editors will side with reviewers regardless of your reasoning. The framework improves your chances of a fair outcome but does not guarantee one. The framework also assumes that you have accurately assessed your constraints. If you decline a request because of resource constraints but the editor believes the resources are available, you may need to provide additional documentation. Be prepared to justify your feasibility assessment. Finally, the framework does not address every possible reviewer request. Some requests raise unique issues that require individualized responses. Use the framework as a starting point and adapt it to your situation. ## Safety and Regulatory Context Some reviewer requests raise safety or regulatory concerns. Animal studies are governed by institutional animal care and use committee approvals. Human studies are governed by institutional review board approvals. Clinical trials are governed by regulatory requirements. If a reviewer requests an experiment that would require new approvals, explain that the approval process is a constraint. The [NIH Grants and Funding portal](https://grants.nih.gov/) describes the regulatory context for NIH-funded research. If your project is NIH-funded, your approved grant application defines the scope of your research activities. Experiments outside that scope may require prior approval from your funding institute. ## Professional Escalation Criteria Know when to escalate a dispute beyond the editor. Escalate when you believe the review process has violated publication ethics. The [Committee on Publication Ethics Core Practices](https://publicationethics.org/core-practices) describe the responsibilities of journals, editors, and reviewers. If you believe these responsibilities have been violated, you may contact the journal directly or use the COPE flowcharts for guidance. Escalate when a reviewer requests data that does not exist or experiments that are impossible. Escalate when a reviewer makes personal attacks or demands inappropriate citations. Escalate when an editor does not respond to your concerns about the review process. ## Frequently Asked Questions ### How do I respond to a reviewer who asks for an experiment that requires funding I do not have? Explain the funding constraint specifically. State that your approved budget does not include the requested work and that additional funding is not available within the project timeline. Reference your original grant application if applicable. The [NIH Grants and Funding portal](https://grants.nih.gov/) describes how research budgets are planned and approved. Offer alternative evidence that addresses the reviewer's concern without the additional cost. ### What if the reviewer asks for an experiment that would take longer than my funding period? Explain the timeline constraint directly. State when your funding ends and why the experiment cannot be completed before that date. If the experiment could be completed after the funding period, explain that you do not have salary support or laboratory access beyond the current award. Propose an alternative that can be completed within your timeline. ### Can I refuse to do an experiment because I think it is scientifically unnecessary? Yes, you can decline a request if you can explain why the experiment is unnecessary. Provide specific reasoning about why the existing data addresses the reviewer's concern. Reference the relevant [reporting guidelines from the EQUATOR Network](https://www.equator-network.org/) if they support your position. Maintain a respectful tone and acknowledge the reviewer's perspective. ### How do I handle a reviewer who repeats the same request after I have already responded? Contact the editor and explain that you have addressed the concern and that the reviewer has not engaged with your response. Provide your original response and the reviewer's repeated request. Ask the editor to mediate. The [Committee on Publication Ethics Core Practices](https://publicationethics.org/core-practices) describe the editor's responsibility to manage peer review fairly. ### Should I add a collaborator to perform a requested experiment? Only add a collaborator if they make a substantial intellectual contribution to the work. Adding someone solely to perform a requested experiment may not meet authorship criteria. The [Committee on Publication Ethics Core Practices](https://publicationethics.org/core-practices) describe authorship requirements. If a collaborator performs the experiment and contributes to interpretation, they may qualify for authorship. ### What if the reviewer asks for raw data that I am not required to share? Consider whether sharing the data addresses the reviewer's concern. If the data supports your conclusions, sharing it may resolve the issue. If your funding requires data sharing, comply with that requirement. The [NIH Data Management and Sharing Policy](https://sharing.nih.gov/data-management-and-sharing-policy) describes expectations for NIH-funded research. If you decline to share data, explain your reasons clearly. ### How do I propose an alternative experiment without seeming dismissive? Frame the alternative as a solution to the reviewer's underlying concern. State that you understand the concern and that the alternative addresses it directly. Explain how the alternative answers the same question the reviewer's experiment would answer. Show that you have thought carefully about what the reviewer needs to see. ### When should I contact the editor about a reviewer request? Contact the editor when the request is unreasonable, when the reviewer is not engaging with your responses, or when you believe the review process is unfair. Provide specific documentation of the problem. The [Committee on Publication Ethics Core Practices](https://publicationethics.org/core-practices) describe expectations for fair peer review that can support your escalation. ## 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 - [Environmental Science Experiments You Can Do: From Air Pollution to Erosion](/blog/careers/environmental-science-experiments-you-can-do-from-air-pollution-to-erosion) - [What Can You Do With a Biology Degree](/blog/news/what-can-you-do-with-a-biology-degree) - [Agriculture Major Jobs: What Can You Do With an Agriculture Degree?](/blog/careers/agriculture-major-jobs-what-can-you-do-with-an-agriculture-degree) - [Observational vs. Experimental Studies: A Decision Framework for Life Science Researchers](/blog/guides/observational-vs-experimental-studies-a-decision-framework-for-life-science-researchers) - [What Can I Do With a Biology Degree](/blog/news/what-can-i-do-with-a-biology-degree) ## 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.