Reviews Of Evidcne

Question 1

What are 2 types of reviews

Answer 1

NArrative: implicit assumptions, opaque methodology, not reproducible -> biased, subjective
Systematic Revews: explicit assumptions, transparent methodology, reproducible -> unbiased, objective

Question 2

How are systematicc rewrites carried out

Answer 2

Explicit statements about: types of study, participants, interventions, outcome measures
Systematic literature search
Selection of the materials
Appraisal
Synthesis (possibly including a meta-analysis)
A systematic review is therefore an extremely credible source of evidence - let aspects are hat it is explicit, transparent and reproducible

Question 3

What is a systematic review and metal analysis

Answer 3

Systematic review: overview o primary studies that used explicit and reproducible methods
A meta-analysis is a quantitative synthesis of the results of 2 or more primary studies that addressed the same hypothesis in the same way
A systematic review will to necessarily include a meta analysis eg i clinical heterogeneity is too great

Question 4

What is the purpose o meta analysis

Answer 4

To facilitate the synthesis of a large umber of study results
To systematically collate study results
To reduce problems if interpretation due to variations in sampling
To quantify effect sizes and their uncertainty as a pooled estimate

Question 5

What are meta analysis quality criteria

Answer 5

Should have a formal protocol specifying
-complication of complete set of studies
Identification of common variable or category definition
Standardised data extraction
Analysis allowing fo sources ofvaiaiton

Question 6

what are ones estimate odds ratios

Answer 6

ORs and 95 CIs are calculated for all studies in metal analysus. These are then combined to give a pooled estimate odds ration using a statisticalcompurer program. Studies are weighte according to their size and the uncertainty f their odds ration (narrower CI ->`Greater weight to result)

Question 7

How to interpret forest plots

Answer 7

Individual ORs (squares) with there 95CI (lines) are displayed. Size of square = weight. The diamond is the pooled estimate with the centre = pooled OR and width = pooled 95% CI. The solid line os the null hypothesis OR

Question 8

What are meta analysis problems

Answer 8

Heterogeneity between studies,
Modelling for variation - fixed effect model s random effects model
Analysisg variation - sub group analysis
Variable quality of studies
Publication bias

Question 9

What are the 2 approaches to calculating the Poole estimate OR and 95% CI

Answer 9

Fixed effects - assumes that the studies are estimating exactly the same true effect size
Random effects model - assumes hat the studies are estimating similar but not the same true effect

Question 10

Compare iced effects vs random effects

Answer 10

S

Question 11

How is variation between studies analysed

Answer 11

Radom effects modelling can only account for variation but not explain it. Sun group analysis can help to explain heterogeneity which may provide further insight into the effect of a treatment of exposure.

• study characterises (eg year of publication, length of follow up, %female participants)
• participant profile - where data is analysed by type o participants (eg subgroups of males, females, adults, children)

Question 12

What ae the issues in variable quality of the studies

Answer 12

Variable quality can be due to 
Asher to assess
- poor study desig 
-poor design protocol 
- poor protocol implementation 
Harder to asses

Some studies are more prone to bias and confounding than others 
Less susceptible
- RCTs
- nRCTS
- cohort 
Case control 
More susceptible

Question 13

What ar the 2 approaches to test quality of the study

Answer 13

Define a basic quality standard and only include satisfactory studies

Score each study for quality and then

• incorporate teh quality sore into th weighting allocated to each study during the modelling, so that higher quality studies have a greater influence on pooled estimate
• used sub-group aalysys to explore differences e.g. high quality studies v slow q

Question 14

What scares are variable too rcts

Answer 14

S

Question 15

Describe publication bias in selection of studies

Answer 15

Statistically significant or favourable results are more likely to be published than those with non stat significant or unfavourable results - this applies particularly to smaller studies

Any systematic review or meta analysis can be flawed by such bias
- publication bias leads to aliased selection of studies towards demonsario of effect

Question 16

What are methods of identification of publication bias

Answer 16

Check meta-analysis protocol for method of identification of studies. It should include searching and identification of unpublished studies
Plot results of identified studies against a measure of their size ie funnel plot
Use a statistical test for publication bias - they tent to be a weak statistical test

Question 17

Ecsirbe a funnel plot

Answer 17

A Plot of some measure o study size against a measure of effect
I fno publication bias, then he plot will be symmetrical
Smaller studies ca be expected to vary frther from central (broader funnel)
Publication bias is likely to exist if there are few small studies with results indicating small or negative measure of effect