Lecture 13 - Reviews Of Evidence (Systemic Reviews And Meta-analyses) Flashcards
What are the 2 types of descriptive studies?
Ecological studies
Cross-sectional surveys
What are the 2 types of analytical studies?
Case control studies
Cohort studies
What are the strongest type of scientific evidence?
Meta-analyses
Systematic reviews
What is primary research?
One study done like an RCT
What is secondary research?
Reviews (so research on research)
What is a narrative review?
Implicit assumptions, opaque methodology and is not reproducible
Its biased and subjective
What are systematic reviews?
Explicit assumption, transparent ,methodology and IS Reproducible
A summary of medical literature on a topic conducted using explicit methods
Its unbiased and objective so BETTER THAN NARRATIVE REVIEWS
What is meta-analysis?
A quantitative synthesis of the results of two or more primary studies (lots of studies) that addressed the same hypothesis in the Same way
What are the criteria for a systematic review?
Explicitly states inclusion and exclusion criteria:
-types of study
-types of participants
-types of interventions
-types of outcome measures
So a clearly focused research question
What is the purpose of a meta-analysis?
Systematically collates study results and to facilitate the synthesis of a large number of study results
This reduces problems of interpretation due to variations in sampling
What is the quality criteria for a meta-analysis?
Complication of complete set of studies
Identification. Of common variable or category definition
Standardised data extraction
Analysis incorporation for sources of variation
How are odds ratios and confidence intervals used in meta analysis?
In meta analysis, odds ratios and their 95% confidence intervals are calculated for all studies and are combined to give a pooled estimated odds ratio
The studies are WEIGHTED depending on their size and uncertainty of their odds ratio (narrower Confidence interval = greater weight to result)
Look at slide 34 at the forest plot,
What does the size of the square represent?
What does the solid line indicate?
What does the diamond and its width indicate?
Size of square = proportional to the weight given to the study
Solid line = null value (1 in this case cuz its risk ratio, would be 0 in mean absolute difference)
Diamond width = pooled 95% confidence interval
Diamond = pooled estimate/dotted line = pled odds ratio
Looking at slide 33 and 34 which test was statistically significant and why?
7 and the meta analysis pooled estimate
The horizontal line for study 7 (which indicates the confidence interval doesn’t cross the null value of 1, so null value isn’t in the confidence interval)
Meta analysis pooled estimates confidence interval is represented by the width of the diamond and it doesn’t cross the null value of 1
What are the 3 key problems in meta-analaysis?
Heterogenity between studies
Variable quality of the studies
Publication bias in selection of studies
What is publication bias?
when you only use studies that support what you want the meta-analysis to support.
What is meant by heterogenity between studies?
The observed effects in the studies are more different than you’d expect by chance
What causes heterogenity between studies?
Differences in methods (study design) methodological heterogenity
Difference in patients, interventions and outcomes (clinical heterogenity)
How does a homogenous forest plot differ to a more heterogenous forest plot?
(Slide 43)
Homogenous = all studies cross the null value solid line
Heterogenous = not all studies cross the null value solid line
How can we count for heterogenity between studies?
What 2 models?
Fixed effect model
Random effects model
What is the fixed effect model?
Assumes that studies are estimating exactly the same true size effect
What is the random effects model?
Incorporates heterogenity by assuming that studies are estimating similar but not the same true effect size
What model should you always use off theres heterogenity between studies?
RANDOM EFFECTS MODEL
How is the confidence interval affected with heterogenity in random effects model than in fixed model?
Confidence interval slightly wider in Random Effects model
What is the problem of the random effects model with heterogenity?
Only incorporates heterogenity and DOESNT EXPLAIN it
What are the issues with the variable quality of the studies in meta-analyyysis?
Poor study design
Poor design protocol
Poor protocol implemtation
What type of studies are more susceptible to bias and confounding?
What types of studies are less susceptible to bias and confounding?
More susceptible = case-control, cohort
Less susceptible = randomised control trials, non-randomised controlled trials
How do you decide what. Studies you’re going to combine in meta—analysis?
Define a basic quality standard and only used them
Score each study for its quality and then incorporate the quality score and allocate it a weight
How can you decide a meta-analysis has been subject to publication bias?
A funnel plot
Loo at slide 66:
Why does the funnel plot on the right side show evidence of publication bias?
There lacking in smaller studies like the other funnel plot
How do you interpret a funnel plot?
Measures study size against measure of effect
If no publication bias then the plot will be balanced if there is publication bias there are going to be fewer smaller studies with results indicating small or negatives measures of effect
