Evidence based medicine 2 Flashcards
4 possible reasons to make decisions
- logic, based on understanding of mech
- personal experience
- advice from others
- data from clinical trials
do we always need clinical trials
no, sometimes it’s obvious or historical
3 examples where treatment seemed obv and wasn’t
- carotid artery bypass
- supression of arrhythmias post MI
- bone density and flouride
what is only way to remove bias
RCT
7 key aspects of RCT
- randomized groups
- groups treated equally apart from intervention
- all subjects accounted for at end
- subjects analyzed based on group they were assigned
- double blind ideal
- all relevent outcomes reported
- consider both clinical and stats. sig.
def. efficacy
does it work in ideal circumstances
def. effectiveness
does it work in real circumstances
2 ways that study must be generalizable
- therapy - are treatments actually done in real life
2. patients - do patient represent real population
4 possible outcome measures
- mortality
- morbidity - hosp., events
- symptomatic status - functional status, Sx releif
- surrogate markers - BP, chol. levels
what are 2 premises of surrogate outcomes
- parameter is risk factor for outcome
2. releif of marker should lower rate of illness
what endpoints are preferred
meaningful endpoints (mort, morbidity, symtoms)
what is metaanalysis
- summarize trials
- convert risk reduction or OR for each trial
- calulate weighted avg.
- if below 1, then better than alternative
what is type 1 error and magniture of sig.
finding a difference when one does not exist (p
what is type 2 error and magniture of sig.
not finding a diff. when one does exist
- magnitude is beta 0.8
what is clinical sig.
is the mag. of the treatment benefit compared to any side effects worthwhile
what is relative risk reduction (RRR)
(risk in untreated - risk in treated)/(risk in untreated) x 100%
what is absolute risk reduction (ARR)
risk in untreated - risk in treated
when are you better off to prescribe
in people that have a higher baseline risk - more absolute risk reduction
what is number needed to treat
number need to treat to affect 1 person
what is formula for NNT
reciprocal of ARR = 1/ARR
how to interpret NNT
- smaller better
- treatment 2-5
- prophylaxis 10-100
what is number needed to harm
same as NNT, but to do some bad outcome
what is balance of NNT and NNH
LHH - likelihood of being helped versus being harmed
