Appraisal of other study types Flashcards
What questions do you need to think about for appraisal of a meta-analysis, in the selection bias bit?
Database used
Data abstraction (min 2 reviewers for inclusion criteria)
Publication bias
Why is publication bias relevant
because studies are more likely to be published if large sample size and strong positive findings > may lead to overestimation of effect
What graphic will show publication bias
A FUNNEL PLOT
What is a funnel plot?
A scatter plot of the intervention effect estimates of each study against that study’s size (n) and precision (CI)
What bit of data abstraction is important?
That each study included is reviewed by TWO reviewers at least
They should each enter it into data abstraction form
Any discrepancies between forms should be assessed by a third person
What concepts matter when pooling results?
HOMOGENEITY vs HETEROGENEITY
conceptual homogeneity > statistical homogeneity (results of different studies should not be combined if not conceptually similar)
What two statistical models can be used to combine results in meta analayses
Random effects model VS fixed effects model
Explain the random effects model
Assumes HETEROGENEITY between studiies (i.e. that they may have different populations with different treatment responsess)
Is MORE CONSERVATIVE, thereby less likelly to show significant results
Explain the fixed effects model
Assumes HOMOGENEITY between studies! I.e. that all studies have the same population and the same response to treatment, and that any difference is simply due to random error
MORE LIKELY TO SHOW STAT SIG RESULTS
Explain a forest plot
Used in meta analyses
Summarises heterogeneity and pooled results of the studies
What do box and diamond represent in a forest plot?
BOX= estimate for a single study (horiz line = confidence intervall) DIAMOND = pooled estimate (width of diamond = confidence interval)
When is it good to use a cohort study over an RCT?
when randomisation of exposure is NOT possibe > either RCT sample will be too large or unethical
When is it good to use a case cotrol study?
If follow up time period is very long Rare outcome (so need for huge sample size otherwise)
What are cross-sectional studies useful for?
Quick and inexpensive > useful in generating and exploring hypothesis that will be subsequently investigated using other study types
What is surveillance bias, and what kind of study would it occur in?
RCT / prospective cohort study
= going to look for disiease that may have gone unnoticed as you think there is a risk
