Inclusion and exclusion criteria
This section contains the following:
Introduction
Every RCT should address an issue relevant to a population with the
condition of interest. Trialists should usually restrict this
population
by using eligibility criteria and by performing the trial in one or a
few centres. Typical selection criteria may relate to age, sex,
clinical diagnosis, and co-morbid conditions; exclusion criteria are
often used to ensure patient safety.
Eligibility criteria should be
explicitly defined.
Careful descriptions of the trial participants and the setting in
which they were studied are needed so that readers may assess the external validity (generalisability) of
the trial results.
Because they are applied before randomisation, eligibility criteria do
not affect the internal validity
of a trial.
Pragmatic RCTs are designed not
only to determine whether the intervention works, but also to describe
all the consequences of its use, good and bad, under circumstances
mimicking clinical practice. To achieve this, pragmatic
studies tend to use more lax criteria to include participants with
heterogeneous characteristics,
similar to those seen by clinicians in their daily practice.
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Things to consider when writing a
protocol
- Specifically state the criteria for centre/participant
inclusion or exclusion in the trial.
- Inclusion and exclusion criteria should be listed
separately.
- Criteria should include details of all relevant
descriptors necessary for eligible centres/participants to be included
in the trial,
or criteria that would disqualify otherwise eligible
centres/participants.
- Such criteria may include: facilities; expertise; patient
numbers; or participants’ age, sex, or health status.
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Illustrative example - Single centre trial
example: from the BMJ 1999
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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.
(adapted from BMJ 1999; 318: 1041-1043 - go to article (included with permission))
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Illustrative example - Multi centre
trial example: WHO pre-eclampsia trial
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Eligibility criteria
Pregnant women attending antenatal care in the participating centres
will be eligible if the following criteria are met:
Randomization will be 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 will be 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.
-
Plan to deliver in a health facility outside the study
area
or at home.
-
Taking phenytoin or tetracyclines.
(WHO Multicentre Randomized Trial of Calcium Supplementation for the
Prevention of Pre-eclampsia - go to protocol)
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Illustrative example - Cluster
trial example: Perinatal care trial
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Inclusion criteria for hospitals
Hospitals will be invited to participate in the study if they fulfil
the following criteria:
-
have an Institutional Review Board (IRB), or existing
committee which could serve as such, or have an agreement with an IRB
which reviews the research protocols implemented in the hospital;
-
have at least 500 vaginal deliveries per year;
-
do not have an explicit policy for selective episiotomy
and
for active management of third stage of labor; and
-
consent to participate in the study.
Those preselected hospitals will perform a baseline data
collection.
According to the results of the analysis of the baseline data
collection, hospitals will be excluded if the episiotomy rate is low or
the rate of
active management is high, according to the following cut-off points:
Because these hospitals do not have a policy for selective episiotomy
or active management, it is expected that none of them will be excluded
by
this criteria. The sample size of the study was increased to
allow
for exclusions. (CLAP Trial - go to protocol)
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Additional resources
This checklist has been contributed by Dave Sackett, who prepared it
for
the forthcoming 3rd edition of Clinical Epidemiology; A Basic Science
for
Answering Questions about Health Care, to be published by Lippincott,
Williams
& Wilkins in 2005.
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This page was last updated 16th December 2003.