7.1 evidence based medicine Flashcards
what is a confounder?
a factor associated with the exposure and is independently a risk factor for the disease
e.g alcohol leads to an MI, but smoking can be a confounding factor
when is blinding difficult?
- surgical procedures
- psychotherapy Vs antidepressants
- alternative medicines e.g acupuncture
- lifestyle interventions
- prevention programmes
what is an explanatory tiral: ‘as treated’ analysis? and what are the weak points?
analyses only those who completed follow up and complied with treatments
compares the physiological effects of the treatments
HOWEVER, loses the effects of randomisation - non compliers are likely to be systematically different from the compliers = selection bias and confounding
what is a pragmatic trial: ‘intention to treat’ analysis?
analyses according to the original allocation to treatment groups (regardless of whether they completed follow up or adhered to treatment)
preserves the effects of randomisation = minimal selection bias and confounding
what are the key differences in as treated Vs intention to treat trials?
As treated = larger sizes of effect = more impressive results
intention to treat = analysis tends to give smaller and more realistic sizes of effect
what are the faults of systemic reviews of trials?
isn’t perfect evidence
just because a trial has been conducted doesn’t mean you should accept its findings
so, do not just report what you read - interpret it and critique it using skills already learnt
what are the faults of randomised control trials?
- defined inclusion/exclusion criteria
- baseline comparability
- defined primary outcome
- good follow up and of adequate length
- sample size calculation
- may be poorly generalisable
- intervention may be poorly reproducible
- may have poor randomisation technique
- may be analysed poorly
- not everything can be tested with a RCT e.g smoking
