Clinical epidemiology: Systematic reviews of RCTs Flashcards Preview

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Flashcards in Clinical epidemiology: Systematic reviews of RCTs Deck (29)
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1
Q

What are some reasons why there are differences between RCTs?

A

Differences:

  • in people compared
  • in care, other than that being investigated
  • in the way treatment effects are assessed
  • in follow up

Available evidence:

  • differences in reporting
  • biased selection

Also obsolescence over time, changes in risk profile of patients, missing information
Hopefully not:
- bad science
- fraudulent science

2
Q

What is a systematic review?

A

Review of all literature on one particular topic using scientific methods:

  • clear question being addressed - PICO
  • explicit and detailed statement of the methods used
  • comprehensive ascertainment of the literature relevant to the review question
  • steps to reduce bias in the review process with or without: a statistical technique used to produce a numerical summary of the size of effect with confidence intervals
3
Q

What are the advantages of systematic reviews?

A
  • can be the best source of evidence on the effects and effectiveness of healthcare interventions
  • assimilate large amounts of research evidence
  • provide reliable unbiased estimates of effect
  • increase precision of estimates of effects
  • provide information about the generalisability and consistency of effects
  • Identify what information is missing
  • Useful for making decisions
4
Q

How does the purpose of a narrative review (non-systematic review) differ from a systematic review?

A

Narrative review:
- background information and current thinking

Systematic review:
- identify, evaluate and summarise current evidence

5
Q

How do the methods of a narrative review (non-systematic review) differ from a systematic review?

A

Narrative review:
- Not specified

Systematic review:
- specified and reproducible

6
Q

How does the review question of a narrative review (non-systematic review) differ from a systematic review?

A

Narrative review:
- often general discussion with no stated hypothesis

Systematic review:
- starts with clear question or hypothesis to be tested

7
Q

How does the identification of studies of a narrative review (non-systematic review) differ from a systematic review?

A

Narrative review:
- well known articles, filling cabinet or selected e.g. medline only

Systematic review:
- planned search strategy for published and unpublished studies

8
Q

How does the study selection for inclusion of a narrative review (non-systematic review) differ from a systematic review?

A

Narrative review:
- do not usually describe why studies are included/excluded

Systematic review:
- explicit criteria for included and excluded studies

9
Q

How does the quality of assessment and data extraction of a narrative review (non-systematic review) differ from a systematic review?

A

Narrative review:
- subjective data extraction, do not usually consider study methods and bias

Systematic review:
- objective extraction of data, critical examination of study methods and bias -standard quality assessment method

10
Q

How does the analysis of results of a narrative review (non-systematic review) differ from a systematic review?

A

Narrative review:
- various; often don’t consider differences between studies

Systematic review:
- Validated methods, assess heterogeneity, meta-analysis

11
Q

What is the first stage of a systematic review?

A

Define question:
- based on a well defined PICO, is the question answerable?, is there already an up to date well conducted systematic review?

12
Q

What is the second stage of a systematic review?

A

Write protocol

  • why is the review important?
  • description of the methods to be used: search strategy, data collection and analysis
  • ensures methods and problems are considered beforehand
  • Reduces the introduction of bias - prevents cheating as the protocol has to be registered
13
Q

What is the third stage of a systematic review?

A

Search for evidence/studies
- Comprehensive identification of relevant studies using: bibliographic databases (medline, embase), grey literature, non-english literature, contact key experts/authors

A good review should look at all languages

14
Q

What is the fourth stage of a systematic review?

A

Select relevant studies from search

  • unbiased selection of studies for review
  • 2 reviewers independently using pre-defined criteria based on PICO to select relevant studies
  • reduce errors and bias - looking at very specific criteria to include/exclude - first you do abstracts then you do full paper
15
Q

What is the fifth stage of a systematic review?

A

Appraise studies

  • unbiased assessment of methodological quality of each study
  • two reviews independently using checklist e.g. CASP
  • reduce errors and bias

Cochrane database have a manual of how to do a systematic review

16
Q

What is the sixth stage of a systematic review?

A

Extract, analyse and summarise data

  • unbiased extraction of relevant data from studies in review
  • 2 reviewers independently using pre-defined approach to identify relevant data in studies
  • pre-defined analysis of data
  • use of validated appropriate methods of numerical data synthesis (meta-analysis)
17
Q

What is the seventh stage of a systematic review?

A

Interpret review results

  • unbiased interpretation
  • considers the results in the context of features and quality of the studies included in the review
  • eg. age of trial may mean the comparator out of date
18
Q

What is the final stage of a systematic review?

A

Discussion and conclusions
- consider implications of review findings in the context of current practice and knowledge and outlines specific future research
Summary of findings

19
Q

In a forest plot, what does the size of the square mean?

A

Relates to the weight given to the study in the review - very affect by SD = dispersion of results within the study

20
Q

In a forest plot, what does the middle of the square mean?

A

represents the result e.g. the relative risk for a study

21
Q

In a forest plot, what does the diamond mean?

A

Summarised result - the width of the diamond represents 95% CI

22
Q

In a forest plot, what does the line in each study mean?

A

the line represents the 95% CI

23
Q

In a forest plot, what does the mid line mean?

A

line of no difference between the trial groups

24
Q

What is the I2 used for ?

A

measuring level of heterogeneity = any variability between studies in a systematic review- could be clinical, methodological, or statistical heterogeneity
<25 = level of difference that doesn’t matter
>75 = worry trials are too different

25
Q

What papers are more likely to be published?

A

Positive results bias - authors are more likely to submit and editors are more likely to accept positive results than negative or inconclusive results

26
Q

What is outcome reporting bias?

A

several outcomes in a trial are reported selectively depending on the strength and direction of those results

27
Q

What is language bias?

A

Positive results and large studies are more likely to be in english
Negative results and smaller studies are less likely to be in english
Sometimes a time lag for non-english studies

28
Q

How can study size influence bias?

A

Small studies most likely to find small non-significant effects
Small studies that find a large effect size (by chance) are more likely to be published
Small studies with non-significant results are less likely to be published

29
Q

What are funnel plots?

A

Scatter plot of the treatment effect size against a measure of each study’s size or precision
- effect size = horizontal
- study size = vertical
Subjective assessment of symmetry