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Epidemiology > Meta analysis. > Flashcards

Meta analysis. Flashcards

1
Q

What sort of review has increased objectivity?

A

Systematic.

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2
Q

What sort of summary does a systematic review provide?

A

Qualitative only.

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3
Q

What sort of bias can be introduced with a systematic review?

A

Publication bias.

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4
Q

What does ‘meta analysis’ refer to?

A

The analysis of analysis.

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5
Q

What does a meta analysis do increased compared to a systematic review?

A

Increase objectivity.

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6
Q

What are the two main limitations of using a single study when looking at research evidence?

A
  1. Poor study design and low numbers will result in false negative results.
  2. Only a subset of the population will be studied.
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7
Q

For studies to be combined what must the treatments used in each studies be?

A

Very similar.

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8
Q

What three questions often drive a meta analysis?

A
  1. What is the average effect of a treatment?
  2. Who benefits most from the treatment?
  3. In what situations will the treatment work?
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9
Q

What is the purpose of producing a review protocol before conducting a meta analysis?

A

To indicate the methods used in advance that aim to minimize the systematic errors.

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10
Q

The inclusion/ exclusion of studies in a meta analysis are defined by PICOS. What does PICOS stand for?

A 
Patient/ population.
Intervention.
Comparison.
Outcome.
Study Design.
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11
Q

What is PRISMA?

A

‘Transparent reporting of systematic reviews and Meta-Analyses’

Provides detailed guidelines regarding the preparation of Meta Analysis.

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12
Q

Fill in the gaps regarding what is includes in a meta-analysis review protocol.

  1. ______ selection.
  2. ______ question.
  3. Study_______ and ______ criteria (PICOS).
  4. Identify ______ _______.
  5. Select _______
  6. ______ data.
  7. ________ assessment
  8. How will study results be _______?
  9. How will results and _______ be presented?
A
  1. Background.
  2. Research.
  3. Inclusion/ Exclusion.
  4. Research evidence.
  5. Studies.
  6. Extract.
  7. Quality.
  8. Synthesised.
  9. Conclusions.
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13
Q

What is the individual unit used in the statistical analysis in a meta analysis?

A

A sample.

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14
Q

What are the two types of goals in a meta-analysis

A
  1. Synthetic goals.

2. Analytical goals.

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15
Q

Describe what synthetic goals are in meta-analysis?

A

To estimate of an overall summary of the average effect across studies while increasing precision by obtaining data from multiple studies.

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16
Q

Describe what analytical goals are in meta-analysis?

A

To identify and estimate differences between study specific effects (heterogeneity) between studies. To track down the source of this variation.

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17
Q

If the endpoint of a meta-analysis is continuous what summary statistics should you calculate?

A

The differences in means and the standard error of this difference/ CI.

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18
Q

If the endpoint of a meta-analysis is binary what summary statistics should you calculate?

A

The log (odds ratio) and its standard error.

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19
Q

If the endpoint of a meta-analysis is a survival endpoint what summary statistics should you calculate?

A

The log (hazard ratio) and its standard error.

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20
Q

What combined effect is shown in the diamond of forest plots?

A

The weighted average of the effects of each study.

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21
Q

What is the weight assigned to each study proportional to?

A

The precision of the study.

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22
Q

What is the equation to determine the weight given to a study in meta-analysis?

A

W=1/variance

23
Q

Why does the effect size vary between studies?

A
  1. Random error.

2. True variation.

24
Q

What model determines the random error of a study?

A

Fixed effect model.

25
Q

What model determines how much true variation there is within a study?

A

Random effect model.

26
Q

What does the fixed effect model (used to determine random variation within a model) assume?

A
  1. All studies in the meta anaylisis are drawn from the same population.
  2. All factors that could influence the effect size are the same in all study populations.
  3. Effect size is the same in all studies. Any variation in effect size between studies is hence due to random error.
27
Q

How does the random effect model differ from the fixed effect model?

A

It assumes that studies were drawn from different populations.

28
Q

What model determines the following?

The combined effect is the estimate of one true effect size.

A

Fixed effect model.

29
Q

What model determines the following?

The combined estimate of effect size is not an average of one value but an average o f a distribution of values.

A

Random effects model.

30
Q

If a fixed effect model gives rise to the best estimate of an assumed common treatment effect what does the random effects model do?

A

Provide a summary result of the average distribution of the of treatment effects across studies.

31
Q

When do you use the random effect model over the fixed effect model?

A

When there is evidence of heterogeneity across studies/ it is likely that heterogeneity is the case.

32
Q

You should decide if your analysis has heterogeneity between studies and use this decision to make a conclusive decision regarding whether you should use a fixed effect or random effect model. True or False?

A

False. It is good practice to present both and examine the difference between the two.

33
Q

How do you do a Cochran’s Q test and why do you do one?

A

Square the deviations of each study estimate from the overall meta analysis estimate. This allows you to determine the weight of the contribution of each study .

34
Q

What distribution does Cochran’s Q test follow?

A

Chi-squared distribution with df of n-1.

35
Q

What statistic test explains the % of variation across studies that can be explained by heterogeneity and not chance?

A

I² test.

36
Q

What are 7 sources of heterogeneity?

A
  1. Differences in statistical analysis.
  2. Differences in populations.
  3. Differences in covariates.
  4. Differences in design and implementation of combined studies.
  5. Heterogeneity of a disease or its classification.
  6. Variation of intervention/exposure measurement and/or definition across studies.
  7. Bias.
37
Q

What are three methods to assess the source of heterogeneity?

A
  1. Analyse different subgroups to see if the results differ.
  2. Perform a sensitivity analysis.
  3. Meta-regression methods.
38
Q

What does the following method describe?

Exclude each study individually and examine the impact that removing each study has on the summary result.

A

Sensitivity analysis.

39
Q

Random effect models are always used when heterogeneity exists between samples in a meta analysis. True or false?

A

False. If too much exists you may not be able to pool the studies.

40
Q

Meta analysis increases the precision of estimates. What can they not eliminate in studies?

A

Bias.

41
Q

What type of scores can reduce bias in a meta analysis?

A

Quality scores.

42
Q

Name two ways in which you can improve study quality in a meta analysis.

A
  1. Only include studies that meet a specified standard quality. Once this decision is made ignore the variation within studies.
  2. Use objective quality-related study characteristics in regression or stratification.
43
Q

Using quality scores in a meta analysis are useful as they are easy to validate. True or false?

A

False.

44
Q

What tool can be used to assess risk of bias in clinical trials?

A

Cochrane Collaboration tool.

45
Q

What 6 forms of bias are mentioned in the Cochrane Collaboration tool?

A
  1. Selection bias.
  2. Performance bias.
  3. Detection bias.
  4. Attrition bias.
  5. Reporter bias.
  6. Other bias.
46
Q

What is attrition bias?

A

Bias caused by incomplete outcome data.

47
Q

What is detection bias?

A

Bias caused by insufficient blinding of participants and personnel.

48
Q

If only a subset of relevant data is available what type of bias is produced?

A

Publication bias.

49
Q

Access to only a limited amount of the available data can cause publication bias. What else can cause publication bias?

A

No reporting of null and non significant findings.

50
Q

What sort of plot can examine the likelihood of bias?

A

A funnel plot.

51
Q

What way round does the funnel have to be on the funnel plot for it to indicate no publication bias.

A

Upside down.

52
Q

What is plotted on the x and y axis on a funnel plot?

A

X- Odds ratio of treatment effect (log scale).

Y- Sample size.

53
Q

What doe the centre of the funnel represent on a funnel plot?

A

The mean effect. The funnel should be symmetric around this.

54
Q

What two things dosystematic literature reviews help you do?

A
  1. Planning new research.

2. Evidence based medicine to set policy..

Epidemiology (14 decks)

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