Patients may participate in trials to “please” their practitioner or because they are “afraid” to refuse.The need for reassurance that future management will not be compromised by non-participation may be greater in primary care, where the patient may see the same practitioner over many years.The appropriateness of general practitioners recruiting their own patients is further complicated if they receive financial rewards for recruiting cases, even if the payment only covers costs.

Ethical trials require both participating clinicians and patients to be in equipoise. Although robust evidence for the cost effectiveness of a particular intervention may not yet exist, if practitioners have a prior belief that one form of management is beneficial they may choose not to randomise patients to treatment.

Beliefs relating to the efficacy, direct effects, or side effects of an intervention affect both doctor and patient participation. Patients who are not prepared to accept randomisation are not eligible to be entered into a trial.The exclusion of patients who refuse endoscopy because they think it is an uncomfortable or painful procedure could affect estimates of the impact of the trial results. Intervention may be cost effective but unacceptable to most patients. Trials of management strategies should aim to determine the proportion of patients who refuse randomisation because of treatment preferences. Complex interventions may require use of additional research tools to assess any barriers to accepting the intervention. (Bradley 1999)