Introduction to EBM and critical appraisal Flashcards
Primary sources of clinical evidence
- peer reviewed journals
- magazines
- newspapers
Secondary sources of clinical evidence
- NHS evidence
- medicines and prescribing from NICE
- guidance from major bodies eg. CKS, SIGN
- published systematic reviews eg Cochrane Library
- MTRAC
Types of studies
- Observational (no intervention)
- cross sectional (survey at one point in time)
- cohort and case control studies
-Experimental (with intervention)
- Controlled trial (parallel, cross over, clusters) RCT, blinding (open single, double blind)
- Systematic review
PICO
Population
intervention
comparator/control
outcomes
p <0.05 =
statistically significant
power
the ability of the study to detect an effect if in truth there is an effect
An RCT may be underpowered if:
- the duration is too short
- it included too few people
- the wrong outcome was used
- expecting a higher level of statistical proof than is realistic for the condition and the intervention being tested
confidence intervals, CI
- the range within which the true value of a population mean lies with a given degree of certainty usually 95%
RRR
the RRR stays constant in different populations
ARR
the ARR alters in different populations - it will be much more impressive if the population has a lot of events
relative risk =
EER/CER
CER =
control event rate, number of events in the control group/total participants in control group [b/ b+d]
EER=
experimental event rate, number of events in the experimental or intervention group/total participants in experimental or intervention group [a/a+c]
Absolute risk difference =
EER - CER
relative risk difference =
(CER - EER)/ CER
