Reviewing The Evidence

Question 1

Systematic reviews
(an extremely credible source of evidence)
“an overview of primary studies that used explicit and reproducible methods”

Answer 1

EXPLICIT, TRANSPARENT AND REPRODUCIBLE 
Clearly focused question 
Explicit statements about the type of study, participants, interventions, outcome measures
Systematic literature search
Selection of the materials 
Appraisal 
Synthesis - meta analysis

Question 2

Meta-analysis

will always include a systematic review

Answer 2

“a quantitative synthesis of the results of two or more primary studies that addressed the same hypothesis in the same way”
- facilitate the synthesis of a large number of studies
- systematically collate study results
- reduces problems of interpretation due to variations in sampling
CI get smaller as there are loads of small studies being analysed together - decreases the effect of chance

Question 3

Calculating a pooled estimate odd ratio for all studies

Answer 3

OR and 95% CI are calculated for all studies in a meta-analysis
They are then combined to give a pooled estimate or using a statistical computer programme
Studies are weighted according to their size and the uncertainty of their OR - smaller would give a greater weighting

Question 4

Forest Plot

Answer 4

Individual odds ratios (squares - size is proportional to their weighting) with their 95% CI lines displayed for each study
The diamond is the pooled estimate - centre (dotted line) is the pooled OR and the width representing the pooled 95% CI. the solid line is the null hypothesis OR

Question 5

Meta-Analysis problems

Answer 5

Heterogeneity between studies
Modelling variation
Variable quality of the studies
Publication bias in selection of the studies
FIXED EFFECT MODEL
- assumes that the studies are estimating exactly the same size effect
- all variation is just random error from the true effect
RANDOM EFFECTS MODEL
- assumes that the studies are estimating similar but not the same effect size
- CI is wider than the fixed effects

Question 6

Publication bias

Answer 6

Studies with significantly significant or favourable results are more likely to be published than those that don’t - applies to smaller studies
- publication bias leads to a biased selection of studies towards demonstration of effect
Meta-analysis should include searching and identification. Of unpublished sucked
FUNNEL PLOTS - the smaller the trail the wider the scatter
- if no bias then the plot will be balanced

Question 7

Evidence based healthcare

Answer 7

Primary research studies RCT
Literature reviews of studies
- narrative reviews (select paper that justifies own viewpoint) - biased and subjective
- systematic reviews (not usually done by a doctor) - unbiased and objective
Decision analysis
- harms vs benefits
- cost effectiveness