Faculty of Health and Medical Sciences

Formulate a Clinical Question

Study types summary

Look up a study type to see information about the clinical question, evidence, strength, sources of bias and timing.


Clinical QuestionTherapy/ Intervention Aetiology Prevention
StrengthKnown and unknown confounders equally distributed between groups
Sources of BiasNo allocation concealment; loss to follow up; analysis by intention to treat; non-blinded outcomes assessment
TimingBegins with study factor: exposure randomized

Cohort Study

Clinical QuestionTherapy/ Intervention Aetiology Prognosis
Sources of BiasLoss to follow up; non-blind assessment of outcome; confounding
TimingBegins with study factor exposure, non randomized

Case-control study

Clinical QuestionTherapy/ Intervention Aetiology
StrengthGood for rare diseases
Sources of BiasRecall bias; confounding; low response rates; non-blind assessment of study factor; controls not chosen from same population as cases
TimingBegins with the outcome of interest

Cross-sectional (diagnostic)

Clinical QuestionDiagnosis
EvidenceBest study to assess accuracy of diagnostic test
Sources of BiasNon-independent blind comparison with gold standard; verification bias; inappropriate spectrum of disease
TimingCompares a diagnostic test to a gold standard

Cross-sectional (analytic)

Clinical QuestionTherapy/ Intervention Aetiology
EvidenceAssociation/ hypothesis generating
StrengthStudy several study/outcome factors at one time to assess association
Sources of BiasSelection of participants non-random (volunteer bias); confounding; low response rates; small sample sizes
TimingStudy and outcome factors measured concurrently