An analysis of factors that predict patient consent to take part in a randomized controlled trial

Recruitment targets of patients to multi-centre primary care-based randomized controlled trials (RCT) are often not met. A critical step in the pathway is whether an eligible patient will give consent.

To assess whether patient, practice or practitioner characteristics are associated with a patient's likelihood of giving consent to participation in a large primary care-based RCT.

A cross-sectional study of patients from 260 practices in England and Wales who met the eligibility criteria for an RCT of aspirin versus warfarin for stroke prevention and attended an appointment with their GP to consider trial participation. Logistic regression analysis was used to determine which patient and practitioner factors independently predicted whether or not a patient would give consent to take part in the trial.

Of the 1740 patients, 973 (55.9%) gave consent. On multivariable analysis, patient factors associated with increased likelihood of giving consent were younger age, current use of warfarin and year of recruitment to the trial. Patients with a history of transient ischaemic attack, angina or valve disease were less likely to give consent. Practice/practitioner factors that were associated with increased likelihood of consent were smaller practice size (practices with greater than eight GPs as compared with those with one to two GPs, odds ratio 0.40, 95% confidence interval 0.21-0.75) and older GPs.

The strong association of consent with year of recruitment may be due to changes in trial procedures and investigator training. If so, this has important implications for the conduct of future trials.