Should You Contact Researchers About Unpublished Studies?

When is it worth asking researchers directly about evidence you cannot find?

You identify a registered study with no publication. A conference abstract never seems to have become a full paper. A funded project appears to have ended years ago without an obvious report. Or a published article mentions another study that no database search can locate.

At some point, searching documents may stop answering the question. The people who conducted the research may know whether the study was completed, whether its findings were published under another title, whether results remain unpublished, or whether additional information can be shared.

Direct contact can therefore complement other methods for identifying unpublished or ongoing studies. The harder question is when that effort is justified and how to do it without turning researcher contact into an informal, selective search that is difficult to reproduce.

Contact researchers when the missing information could matter

What researcher contact can add to an unpublished-evidence search

Contact can help identify studies that other sources cannot resolve

There is no single reliable source containing every completed but unpublished study. The current Cochrane Handbook therefore includes contacting relevant individuals and organizations among methods for identifying unpublished and ongoing research. It describes such contact as highly desirable for intervention reviews when relevant.

Researchers may know about their own unpublished studies, related projects conducted by colleagues, terminated studies, manuscripts in preparation, conference studies that changed title before publication, or other research that is difficult to trace through conventional databases.

This can be particularly useful in small research areas where only a limited number of groups conduct most of the relevant work.

Contact researchers after you have something specific to ask

A focused request is generally more useful than an open-ended message asking whether someone has “anything unpublished.” Before contacting an investigator, gather the information you already have.

For example, you might provide a trial registration number and ask whether results have been published. You might identify a conference abstract and ask whether a full report exists. You could describe your eligibility criteria and ask whether the researcher knows of additional completed or ongoing studies meeting them.

Cochrane suggests that review teams can send researchers a list of studies already identified together with the review's eligibility criteria and ask whether they know of additional relevant studies. This approach reduces ambiguity about what you are actually looking for.

Researcher contact can answer different questions

Not every contact request serves the same purpose. Be clear about what information you need.

Contacting authors can sometimes produce genuinely new information

Researcher contact is not merely a theoretical recommendation. Empirical work has found that author correspondence can provide information unavailable in published reports.

In one case study, Cooper and colleagues contacted authors associated with 88 records from a systematic review. Of 83 possible contacts, 38 replied, a response of approximately 46%. The entire contact process took just under seven hours of researcher time spread across seven weeks, and the authors identified information in replies that was not available in the original publications.

That result should not be treated as a universal response rate or cost estimate. The yield will vary with field, age of studies, contact details, request complexity, researcher engagement, and many other factors. It does show why author contact can sometimes be worth attempting rather than being dismissed as inevitably unproductive.

Ask neutrally rather than searching specifically for disappointing results

If your concern is publication bias, avoid contacting researchers with a question such as, “Do you have any negative studies you did not publish?” That framing assumes something about the missing evidence and may itself produce selective retrieval.

Instead, describe the eligibility criteria and ask about relevant completed, terminated, ongoing, or unpublished research regardless of the direction of its results. This is especially important when attempting to find negative or null studies that never reached publication.

Whom should you contact?

The corresponding author is an obvious starting point for a known publication, but the most appropriate person depends on the problem. For a registered trial, the principal investigator or study contact may be more useful. For an older project, another investigator or the institution may have current contact information.

Cochrane also recognizes contact with experts, organizations, manufacturers, and others with relevant knowledge. PRISMA-S similarly treats contacts with authors, experts, manufacturers, and other parties as a search method that should be reported.

The aim is not to email every person whose name appears in your search results. Target people who have a plausible connection to unresolved eligible evidence.

What should the request contain?

A useful message should make it easy for the recipient to understand what you need. Identify the review or project briefly, explain why you are contacting them, identify the study or project where applicable, state your eligibility question, and ask for specific information.

If you are requesting unpublished numerical data, specify the outcome, time point, analysis population, summary statistic, and any other details needed for interpretation. Asking simply for “the missing data” creates unnecessary correspondence and increases the risk of receiving information that cannot be used.

When asking about additional unpublished studies, provide enough eligibility information for the researcher to distinguish relevant studies from merely related work.

Should you send reminders?

A single unanswered email need not end the attempt. Contact information may be outdated, and messages are easily overlooked. A predefined reminder procedure can improve consistency, such as one follow-up after a specified interval.

There is no universal number of reminders appropriate to every review. Excessive repeated contact can burden researchers and consume review resources. Decide the procedure in advance where practical and apply it consistently to comparable cases.

Information supplied privately still needs verification

If a researcher identifies another study, treat it as a lead and verify what you can. Establish whether it meets your eligibility criteria, whether a public report exists, whether it duplicates another record, and what information can appropriately be used.

If unpublished numerical results are supplied directly, preserve their provenance. Record who provided the information, when it was received, what was requested, and how it entered the analysis.

Do not silently transform private correspondence into apparently published evidence.

Selective responses can create another layer of missingness

Suppose ten investigators are contacted and only four reply. The four responses may add useful evidence, but you do not know whether the six non-respondents would have supplied systematically different information.

This does not make contacting researchers invalid. It means that author contact does not magically eliminate publication bias. It can reduce uncertainty while introducing its own limitations.

Report the contact process transparently

PRISMA-S recommends reporting whether authors, experts, manufacturers, or others were contacted to identify additional studies or data. Because contact strategies can be difficult to reproduce, the guidance recommends describing what information was sought, whom or what groups were approached, and how contacts were identified.

Cochrane likewise recommends documenting correspondence and search decisions. Keep a contact log containing dates, recipients, purpose, reminders, responses, and relevant information obtained.

This record is particularly valuable when a review is updated months or years later and someone inevitably asks, “Did we ever hear back from that investigator?” Academic archaeology is easier when somebody kept notes.

How researcher contact can resolve an apparently unpublished study

Common mistakes when contacting investigators

Use contact strategically rather than automatically

Researcher contact is most defensible when there is a concrete information gap and resolving it could change study eligibility, provide otherwise unavailable evidence, clarify publication status, or materially improve interpretation.

Researcher contact has a cost in time for both the review team and the people being contacted. It should therefore be integrated into the broader decision about how much effort to spend chasing unpublished evidence.

Before contacting a researcher about unpublished evidence

Questions about contacting researchers for unpublished studies

Contact researchers when correspondence can resolve consequential uncertainty

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