If two groups receive different wound treatments, how can researchers tell whether the device mattered or whether the groups simply started out different? Randomization offers one answer: assign participants or wounds by chance, so known and unknown differences are less likely to favor one treatment systematically. It cannot make a small trial conclusive, but it can make a comparison fairer.
The problem of unequal starting points
People entering a study may differ in age, health, wound size, or other factors that influence healing. If clinicians choose who receives a device, those differences can become tangled with the treatment itself. For example, a clinician might understandably offer a promising new device to patients whose wounds seem most suitable. If outcomes later differ, the result may reflect the selection as much as the device.
Randomization uses chance to allocate participants, treatment sessions, or wounds to groups. In expectation, it distributes differences across groups rather than letting a person’s judgment determine assignment. It does not guarantee identical groups, especially in a small study; it reduces a predictable source of bias. Researchers must still describe who participated, what care each group received, and how outcomes were assessed.
A wound trial, step by step
A randomized, placebo-controlled trial of cold atmospheric plasma (CAP) for diabetic foot ulcers compared standard care plus plasma applications with standard care plus a placebo procedure. The study randomized wounds separately, and participants could contribute wounds to both groups. That design helps illustrate why the unit of assignment matters: a trial may allocate people, body sites, or individual lesions, and these choices shape what the comparison means. [1]
The trial reported greater wound-area reduction in the CAP group on its primary analysis, while infection and microbial-load reductions were not significantly different. Those are distinct outcomes: a change in wound size is not the same finding as a measured change in infection. The study’s randomized design strengthens the comparison, but it does not erase limits such as sample size, setting, or uncertainty about how results generalize. [1]
Blinding and measurement
Blinding means keeping participants or assessors unaware of which treatment was assigned, when practical. It can reduce expectation effects: a patient’s belief about a device may influence subjective reports, and an assessor’s expectations may affect judgments about a wound’s appearance. A placebo procedure can make groups’ experiences more alike, although a device’s sensation or visible operation may make blinding difficult.
Outcome definitions also matter. “Healing” could mean complete closure, a threshold reduction in area, or a change in microbial load. These measures answer different questions and may behave differently over time. In a trial of venous leg ulcers, the listed primary outcome was the percentage of wounds healed; secondary outcomes included wound-area reduction and adverse events. The differences between treatment and control groups in healed proportions were not statistically significant, despite numerically higher percentages in treatment groups. [2]
What a fair test can and cannot say
Randomization supports a causal comparison within the study conditions; it does not prove that every patient will benefit or that a device is ready for routine care. A 2023 guideline from the International Working Group on the Diabetic Foot recommends against using other gases, including CAP, to promote diabetic foot-ulcer healing because the available evidence is low-certainty and at risk of bias. That recommendation emphasizes why individual positive findings must be read alongside the full evidence base. [1] [3]
A useful mental check is to ask: were groups assigned by chance, were outcomes defined before interpretation, and do the reported measures match the claim? A careful trial can reduce alternative explanations, while replication and broader evidence establish whether a result holds across settings. Fair comparison is a method for learning, not a stamp of effectiveness.
Sources & further reading
- Cold Atmospheric Plasma for Diabetic Foot Ulcers: Randomized Trial Stratmann et al., JAMA Network Open (2020)
- Direct Cold Atmospheric Plasma for Venous Leg Ulcers: Randomized Trial Smits et al., Advances in Wound Care (2024)
- Guidelines on Interventions to Enhance Healing of Foot Ulcers: 2023 Update International Working Group on the Diabetic Foot
Prepared for the independent PSI Center reading library. About edition dates and source checking.
This explainer describes scientific principles. It does not assess individual treatment choices.
