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Critical Appraisal > Evidence Based Medicine > Flashcards

Evidence Based Medicine Flashcards

1
Q

What is a confounding factor?

A

Confounder is associated with exposure but not a consequence of exposure. Also associated with outcome independent of exposure

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2
Q

Types of selection bias

A

Recruitment of unrepresentative sample population

  • Sampling bias
  • Response bias
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3
Q

Attrition bias

A

Number of dropouts differ significantly in different arms

Reduced with intention to treat analysis

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4
Q

What is a cohort study?

A
  • observational study
  • group of ppl followed over time to establish incidence of a condition
  • identify risk factors for certain condition
  • prospective or retrospective
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5
Q

What are the advantages of a cohort study?

A
  • demonstrate an appropriate temporal relationship between exposure and outcome
  • estimate incidence rates in exposed and non-exposed groups
  • can assess multiple outcomes
  • can study uncommon exposures
  • insight into latent and incubation periods for communicable/non-communicable diseases
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6
Q

What are the disadvantages of cohort study?

A
  • require large sample size
  • long follow-up periods
  • frequent re-evaluation of exposure
  • portion of cohort lost to FU
  • outcome misdiagnosed/misallocated if diagnostic criteria changed over time
  • outcome assessment vulnerable to diagnostic suspicion bias
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7
Q

What are the disadvantages of cohort study?

A
  • require large sample size
  • long follow-up periods
  • frequent re-evaluation of exposure
  • portion of cohort lost to FU
  • outcome misdiagnosed/misallocated if diagnostic criteria changed over time
  • outcome assessment vulnerable to diagnostic suspicion bias
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8
Q

What is a CONSORT statement?

A

Consolidated Standard of Reporting Trials

set of recommendations for papers reporting the results of randomised clinical trials.

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9
Q

What guidance does the statement provide?

A
  • 25 item check list
  • template participant flow diagram
  • guidance for each section of paper (abstract, intro, methods, results, discussion, other information
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10
Q

What is a PRISMA statement?

A

Preferred Reporting Items for Systematic Review and Meta-Analysis

Set of evidence-based guidelines intended to improve quality of reports for systemic reviews

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11
Q

What guidance does PRISMA provide?

A
  • 27 item check list
  • Template flow diagram diagram to describe the identification and inclusion/exclusion of trials/studies in the review.
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12
Q

What is impact factor?

A

Measure of a particular journal’s relative importance in its field

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13
Q

How do you calculate impact factor?

A

Number of citations in a given year / number of articles published

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14
Q

Any other bibliometrics similar to impact factor?

A
  • Immediacy index
  • Cited half-life
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15
Q

What is h-index?

A

a simple metric that provides a guide to an individual researcher’s impact on the field

It is the rank of the paper at which position in ranking equals citaiton count

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16
Q

Outline 1 a, b, c of oxford system for studies of intervention

A

1a: systematic reviews or RCT
1b: high quality RCTs with narrow CI
1c: all or nothing RCTs

17
Q

Outline 2 a, b, c of oxford system for studies of intervention

A

2a: systematic review of cohort studies
2b: individual cohort study or low quality RCT
2c: Ecology studies

18
Q

Outline 3 a, b of oxford system for studies of intervention

A

3a: systematic reviews of case control studies
3b: individual case-control studies

19
Q

Outline level 4 and 5of oxford system for studies of intervention

A

4: case series, poor quality cohort or case control study
5: expert opinion

20
Q

Alternative systems to classify level of evidence

A

NICE

SIGN (Scottish intercollegiate guideline network)

21
Q

What is a meta-analysis?

A

Use of statistical methods to combine results of individual studies

22
Q

What is systematic review?

A

Literature review conducted according to strict protocol to identify studies relevant to question under consideration

23
Q

What elements comprise a good systematic review/ meta-analysis?

A
  • well-constructed clinical question in PICO terms
  • objective inclusion and exclusion criteria
  • Key outcomes defined
  • Structured search strategy
  • Efforts to obtain missing data to avoid publication bias
  • Data should be extracted by two or more observers independently using a prepared extraction pro forma
24
Q

What are commonly used pooled outcome measures in meta-analyses?

A
  • Weighted mean difference: continuous variables
  • Pooled odds ratio: categorical variables in interventional studies
  • Risk ratio/ relative risk: categorical variables in epidemiological studies
24
Q

What are commonly used pooled outcome measures in meta-analyses?

A
  • Weighted mean difference: continuous variables
  • Pooled odds ratio: categorical variables in interventional studies
  • Risk ratio/ relative risk: categorical variables in epidemiological studies
25
Q

What are the advantages of meta-analysis compared to traditional literature reviews?

A
  • evaluation for bias
  • greater statistical power to detect effect over single study
  • can control between study variation
  • more reliable synthesis of literature, reduce info overload
  • less likely influenced by local factors
26
Q

Disadvantages to Meta-analysis

A
  • vulnerable to publication bias
  • pooling of several small studies may not predict results of large study
  • unreliable results if source studies poorly designed
27
Q

What is publication bias?

A

Studies with positive results more likely to be published than those with negative results

28
Q

How is publication bias detected?

A

Using a funnel plot

29
Q

Describe a funnel plot

A

X-axis: sample size

Y-axis: effect size (standard error of effect estimate)

30
Q

How to identify publication bias from funnel plot?

A

asymmetric funnel

31
Q

Possible causes of asymmetrical funnel plot

A
  • Publication bias
  • Heterogeneity
  • Poor methodology leading to inflated effects in smaller studies
32
Q

What is a forest plot

A

graphical representation of data from a meta-analysis

33
Q

Describe the format of a forest plot

A

Box: effect estimates form single studies

Diamond: pooled result

Horizontal line: confidence interval

Vertical line: line of no effect

34
Q

What is stratification?

A

a method of ensuring an equal distribution of key confounding factors between arms of a randomised trial

Critical Appraisal (2 decks)

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