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Table 1 RCT Recruitment Terminology

From: The external validity of published randomized controlled trials in primary care

Term Definition
Target population Location and characteristics of potentially eligible individuals, representing the patient population to whom the results of the RCT are expected to apply
Eligibility fraction Proportion of potential participants who undergo screening and are eligible to enrol in the RCT
Enrolment fraction Proportion of people who are eligible for participation and who actually enrol in the RCT
Recruitment fraction Proportion of potential participants who actually enrol in the RCT
Number of patients needed to be screened (NNS) Number of patients screened in order to randomise one participant (equal to 1/recruitment fraction)