Recruitment - Is the participant eligible?

This section contains the following:

Introduction
Things to consider
Illustrative example 1
Illustrative example 2
Additional resources
Further reading

Introduction

Clear eligibility criteria should have been discussed and set out in the trial protocol. Typical selection criteria may relate to age, sex, clinical diagnosis, and co-morbid conditions; exclusion criteria are often used to ensure patient safety. They should have been explicitly defined to answer the study question.

Pragmatic RCTs are designed not only to determine whether the intervention works, but also to describe the circumstances mimicking clinical practice. To achieve this, pragmatic studies tend to use wide criteria to include participants with heterogeneous characteristics, similar to those seen by clinicians in their daily practice.

Things to consider

This checklist has been contributed by Dave Sackett. It is in the 3rd edition of Clinical Epidemiology; A Basic Science for Answering Questions about Health Care, published by Lippincott, Williams & Wilkins in 2005.

Patient eligibility criteria should match your trial question.
Make sure they exclude patients who cannot help you answer your trial question.
Make sure they are objective and unambiguous by achieving “almost perfect” agreement when they are applied by different clinicians to the same patients.
Anticipate sample size requirements and begin to consider strategies for achieving them.
Generate clinician eligibility criteria for potential collaborators
Create your patient-entry forms.
Decide how to handle “eligible but not randomized” patients
Decide how to handle patients whose ineligibility is not discovered until after they are randomized
Decide whether and how to carry out a ‘dry-run’ of your forms and systems
See whether what you have done so far is consistent with your trial question
Set up the “patient-flow” diagram.

Illustrative example - Single centre trial example: from the BMJ 1999

Inclusion criteria

Consecutive patients admitted after a snake bite and require antivenom serum due to systemic envenomation or severe local envenomation.

Exclusion criteria

Patients will be excluded from the study if they are;

pregnant
aged under 12 or over 70 years
said they had received antisera, including antivenom serum, in the past
had known adverse reactions to adrenaline, atopy, wheezing, hypertension, ischaemic heart disease, transient ischaemic attacks, strokes, or unexplained focal neurological signs
had received any treatment other than first aid before admission.
or if electrocardiography on admission shows ischaemic changes or arrhythmias.

Antivenom trial - go to publication

Illustrative example - Multi centre trial example: WHO pre-eclampsia trial

Eligibility criteria
Pregnant women attending antenatal care in the participating centres were eligible if the following criteria are met:

Gestational age <20 weeks
Nulliparous
Capable of giving informed consent. (Informed consent for minors will be obtained following country specific age limits)

Randomization was conducted during the first ANC visit before 20 weeks of gestation. It was decided to include all nulliparous women regardless of their gynaecological history or early pregnancy complications (such as threatened abortion or hyperemesis gravidarum) to cover a high-risk group most readily identifiable. Although there are other risk factors such as positive family history and pre-eclampsia in a previous pregnancy, the screening process to identify these cases is likely to be cumbersome and will be difficult to implement given the diverse populations included in the trial.

Exclusion criteria
Women were excluded under the following conditions:

History of urolithiasis or symptoms suggestive of urolithiasis or any renal disease such as haematuria, flank pain, etc.
Parathyroid disease.
Blood pressure ≥ 140mmHg systolic or ≥ 90mmHg diastolic, receiving treatment or had history of hypertension.
Taking diuretics or any digoxin treatment.
Taking phenytoin or tetracyclines.

WHO Pre-eclampsia trial - go to publication

Additional resources

Consort flow diagram

Consort diagram showing the flow of participants through each stage of a randomised trial.