3a: Eligibility criteria for participants
3b: The settings and location where the data were collected
The study participants
3(a) Eligibility criteria for participants
Example
"… all women requesting an IUCD [intrauterine contraceptive device] at the Family Welfare Centre, Kenyatta National Hospital, who were menstruating regularly and who were between 20 and 44 years of age, were candidates for inclusion in the study. They were not admitted to the study if any of the following criteria were present: (1) a history of ectopic pregnancy, (2) pregnancy within the past 42 days, (3) leiomyomata of the uterus, (4) active PID [pelvic inflammatory disease], (5) a cervical or endometrial malignancy, (6) a known hypersensitivity to tetracyclines, (7) use of any antibiotics within the past 14 days or long-acting injectable penicillin, (8) an impaired response to infection, or (9) residence outside the city of Nairobi, insufficient address for follow-up, or unwillingness to return for follow-up" (74).
Explanation
Every RCT addresses an issue relevant to some population with the condition of interest. Trialists usually restrict this population by using eligibility criteria and by performing the trial in one or a few centers. Typical selection criteria may relate to age, sex, clinical diagnosis, and comorbid conditions; exclusion criteria are often used to ensure patient safety. Eligibility criteria should be explicitly defined. If relevant, any known inaccuracy of patients' diagnoses should be discussed because it can affect the power of the trial (75). The common distinction between inclusion and exclusion criteria is unnecessary (76).
Careful descriptions of the trial participants and the setting in which they were studied are needed so that readers may assess the external validity (generalizability) of the trial results (see item 21). Of particular importance is the method of recruitment, such as by referral or self-selection (for example, through advertisements). Because they are applied before randomization, eligibility criteria do not affect the internal validity of a trial, but they do affect the external validity.
Despite their importance, eligibility criteria are often not reported adequately. For example, 25% of 364 reports of RCTs in surgery did not specify the eligibility criteria (77). Eight published trials leading to clinical alerts by the National Institutes of Health specified an average of 31 eligibility criteria specified in trial protocols. Only 63% of the criteria were mentioned in the journal articles, and only 19% were mentioned in the clinical alerts (78). The number of eligibility criteria in cancer trials increased markedly between the 1970s and 1990s (76).
3(b) The settings and locations where the data were collected
Example
"Volunteers were recruited in London from four general practices and the ear, nose, and throat outpatient department of Northwick Park Hospital. The prescribers were familiar with homoeopathic principles but were not experienced in homoeopathic immunotherapy" (79).
Explanation
Settings and locations affect the external validity of a trial. Health care institutions vary greatly in their organization, experience, and resources and the baseline risk of the medical condition under investigation. Climate and other physical factors, economics, geography, and the social and cultural milieu can all affect a study's external validity.
Authors should report the number and type of settings and care providers involved so that readers can assess external validity. They should describe the settings and locations in which the study was carried out, including the country, city, and immediate environment (for example, community, office practice, hospital clinic, or inpatient unit). In particular, it should be clear whether the trial was carried out in one or several centers ("multicenter trials"). This description should provide enough information that readers can judge whether the results of the trial are relevant to their own setting. Authors should also report any other information about the settings and locations that could influence the observed results, such as problems with transportation that might have affected patient participation.
Page last edited: 23 July 2007
