Evidence-appraisal glossary
Channeling bias
Channeling bias is a distortion in drug studies where prescribers steer certain patients (often sicker, higher-risk, or those who failed other treatments) toward a specific medication. Because those patients differ in prognosis before treatment starts, comparisons with other drugs can wrongly credit or blame the drug for outcomes.
Also called: Channelling bias, Prescription channeling, Channeling (confounding by indication).
What it is
Channeling bias is a form of confounding by indication seen mainly in non-randomized (observational) drug studies. When a new or "safer" drug appears, clinicians tend to "channel" particular patients toward it, for example those with more severe disease, more prior side effects, or worse baseline prognosis. Those patient differences, not the drug itself, can then drive the measured outcome.
How to use it when reading a study
- Ask why patients received one drug versus the comparator. If prescribing was steered by severity or risk, suspect channeling.
- Compare baseline tables. Look for imbalances in disease severity, comorbidity, and prior treatment between groups.
- Check whether authors adjusted for these factors (multivariable models, propensity scores, active-comparator or new-user designs) and whether important confounders could still be unmeasured.
- Note the direction: channeling sicker patients toward a drug can make it look falsely harmful; channeling healthier patients can make it look falsely beneficial.
- Randomized trials largely avoid this, so weigh observational claims accordingly.
This is a plain-language methodology definition for reading research. It is general education, not medical advice.