This, in turn, could bias the estimate of the effect of treatment produced by the trial. Although investigators may not intend to modify their behaviour in these ways,

such effects could even happen subconsciously. However, if the upcoming allocation is concealed from the enrolling investigator, these effects cannot occur. After a patient has been approached and has expressed some interest in participating in the trial, an investigator FK228 cost must determine whether the patient meets the eligibility criteria. Some eligibility criteria (eg, age, gender, the presence of a prosthetic joint) may be clear cut with little opportunity for interpretation. However, other eligibility criteria may be more subjective. For example, in a trial of home-based exercise training for people with chronic heart failure by Chien et al (2011), one exclusion criterion was a primary musculoskeletal disease [affecting] the assessment of exercise capacity. All selleck screening library musculoskeletal diseases will fall somewhere on a spectrum from substantially impairing the assessment of exercise capacity to having no effect. In assessing each potential participant against this criterion, the enrolling investigator

may be forced to decide subjectively whether borderline impairment is negligible or not. Knowledge of the upcoming allocation could affect (consciously or subconsciously) the decision about the patient’s eligibility. Similar motivations to those discussed above could again systematically influence which patients are allocated to each group. For example, patients with a poor prognosis may be deemed ineligible when the upcoming

allocation is to the treatment group but deemed eligible otherwise. Concealment of the allocation list prevents this potential source of bias between the groups. Patients who are deemed eligible for a trial must make a fully informed decision about their willingness to participate (World Medical Association 2008). While a comprehensive description of all the salient points must be given to each interested patient, a standard text is not usually used to guide the description. Because the description can vary between patients, there is again opportunity for knowledge of the upcoming randomisation to affect how the enrolling investigator next describes trial participation to the patient. For example, the negative aspects of trial participation may be emphasised if the investigator wants to divert the patient away from the upcoming allocation. Such negative aspects may include the number of visits required for outcome assessment, the possibility of randomisation to the control group, and the time, effort and expense of undertaking the intervention. Conversely, positive aspects – such as the opportunity to receive the results of health-related tests that would be undertaken as part of outcome assessment – could be emphasised.