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Hierarchy of evidence
Grade I: properly randomised controlled trial.
Grade II-1a: well-designed controlled trial with
pseudo-randomisation.(‘Pseudo-randomisation’
refers to alternate allocation, allocation by birth
date or case-note number.)
Grade II-1b: well-designed controlled trial without
randomisation.
Grade II-2a: well-designed cohort prospective study
with concurrent controls.
Grade II-2b: well-designed cohort prospective study
with historical controls.
Grade II-2c: well-designed cohort retrospective
study with concurrent controls.
Grade II-3: well-designed case–control retrospective
study.
Grade III: large differences from comparisons
between time and/or places with and without
intervention (in some circumstances these may
be equivalent to grade I or II).
Grade IV: opinions of respected authorities,
based on clinical experience, descriptive studies,
or reports of expert committees.
Study design checklist for
assessing validity
RCTs
1. Was the assignment to the treatment groups
really random?
2. Was relatively complete follow-up achieved?
3. Were the outcomes of people who withdrew
described and included in the analysis?
4. Were those assessing outcomes blind to the
treatment allocation?
5. Were the control and treatment groups
comparable at entry?
6. Were groups treated identically other than
for the named intervention?
Cohort studies
1. Are the exposed people representative of the
standard users of the intervention?
2. Was the non-exposed cohort selected from
the same population as the exposed cohort?
3. What confounding factors may affect
the outcome?
4. Were these confounding factors controlled for?
© Queen’s Printer and Controller of HMSO 2002. All rights reserved.
Appendix 3
Health Technology Assessment 2002; Vol. 6: No. 30
Quality criteria for published studies
5. Was the outcome assessment blind to
exposure status?
6. Was an adequate proportion of the cohort
followed up?
Case–control studies
1. Was the disease state of the cases reliably
assessed?
2. Was there a potential for selection bias?
3. Were controls selected from a similar
population as the cases?
4. Were hazards and interventions assessed
in the same way for cases and controls?
5. Was follow-up long enough?
Longitudinal surveys or case series
1. Is the study based on a random sample
selected from a suitable sampling frame?
2. Is there any evidence that the sample is
representative of standard users of
the intervention?
3. Are the inclusion criteria clearly defined?
4. Was follow-up long enough?
5. Were outcomes assessed objectively?
Quality assessment of patient-based
outcome studies 49
Outcome measures for clinical trials should be
chosen by evaluating evidence about instruments
in relation to the following eight criteria.
• Appropriateness: is the content of the
instrument appropriate to the questions which
the clinical trial is intended to address?
• Reliability: does the instrument produce
results that are reproducible and internally
consistent?
• Validity: does the instrument measure what it
claims to measure?
• Responsiveness: does the instrument detect
changes over time that matter to patients?
• Precision: how precise are the scores of the
instrument?
• Interpretability: how interpretable are the
scores of an instrument?
• Acceptability: is the instrument acceptable
to patients?
• Feasibility: is the instrument easy to administer
and process?
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