First published 7 March 2026
No Evidence? No Problem. Why you still can (and should) do Evidence-Based Guidelines
I am not a clinician but a guideline methodology expert; you can read my full disclaimer here.
I hear this a lot when working with guideline development groups:
“There’s no evidence for this, so this should just be a guideline based on expert opinion. No need to do the reviews.”
Often, people assume that because they haven’t come across evidence, it simply doesn’t exist. Sometimes the evidence they did see didn’t support their hypothesis, so they conclude that there is “no evidence” to support their beliefs. Either way, the temptation is the same: skip the systematic approach, rely on expert opinion, and move on. After all, systematic reviews are time-consuming and expensive.
But there are good reasons why every recommendation should still be underpinned by a systematic review.
1. Transparency
A systematic review documents exactly what was searched for, and what was and wasn’t found. When a systematic review concludes that “there is no evidence,” what it really means is: “We looked. Systematically. And we didn’t find anything that met the inclusion criteria”. This transparency matters. By clearly describing the methods used, including search strategies and inclusion criteria, others can understand the scope of the work, the limits of current knowledge, and the basis for the recommendation.
Without this step, “no evidence” can easily mean: “We didn’t check properly”, or “ The evidence didn’t fit our narrative”.
If, truly, no evidence exists, the recommendation may still ultimately be based on expert opinion, but the difference is that this is made explicit. Because the certainty of evidence is very low, the guideline group is more likely to issue a weaker recommendation or a good practice statement. This is an important distinction.
2. Driving research forward
If guideline development groups don’t clearly signal where evidence is lacking, there is little hope of ever filling those gaps. A guideline that explicitly states “evidence gap here” does something powerful: it gives researchers a direction. Evidence-based guidelines are not only about telling people what to do today. They also shape the evidence base for tomorrow.
If guideline groups quietly default to expert opinion without documenting the uncertainty, they effectively close the door on progress. When the guideline is updated years later, nothing has changed, because no one knew these questions needed answering.
3. You might be surprised
Sometimes you expect to find nothing, and you still find something useful. Not necessarily a large randomised trial. Sometimes the evidence is indirect, observational, or incomplete. But it can still provide valuable insights.
For example, in work on Rituals and Behaviours in Operating Theatres, the guideline development group did not expect to find much evidence for some recommendations. And largely, they were right. But structured searching for a question about scrubs being worn outside theatres revealed something interesting. Several studies described the difficulties of conducting research in this area, including compliance problems and logistical barriers. One study revealed an issue that was surprisingly simple: clean scrubs were not always consistently available. If the hospital cannot get the logistics right, it becomes difficult to expect perfect compliance. In that context, the absence of strong evidence for or against a practice becomes much easier to understand.
A similar issue appeared in norovirus guidelines. One research group attempted an ambitious randomised trial comparing different levels of outbreak control measures in nursing homes. In practice, once an outbreak began, institutions assigned to the lower-intervention arms abandoned their protocols and implemented additional measures. Hardly surprising. When an outbreak occurs, staff will do whatever they believe might control it. From a practical and ethical standpoint, it is unrealistic to expect strict adherence to a restrictive research protocol.
These insights were extremely valuable for implementation planning and making recommendations. They highlighted behavioural and system-level constraints that are rarely captured. Had the guideline groups skipped the reviews because “there’s no evidence,” they would have missed information that fundamentally improved how recommendations were made to align with work in real-world settings. Even small details can make recommendations far more realistic and implementable.
So my point is this
Robustness does not come from skipping steps. The evidence may genuinely not exist. Guideline groups cannot control that. What they can control is the process: systematically searching for what exists and being transparent about what does not.
In the absence of evidence, expert opinion is still valid within evidence-based guidelines. The difference is that the opinion is framed by what is known and unknown, and expressed through a structured and transparent discussion, not by whoever speaks the loudest in the room.
So next time you hear someone say: “There’s no evidence here”, remember: the evidence you don’t find can be just as important as the evidence you do.
Doing the systematic work makes your guideline stronger, your recommendations more transparent, and your research agenda clearer.
No evidence? No problem. Evidence-based guidelines are not about having perfect evidence. They are about being honest about the evidence we have and the evidence we don’t.