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Epidemiology and Biostatistics > Meta Analysis > Flashcards

Meta Analysis Flashcards

1
Q

Definition of meta-analysis

A

Technique for combining the findings from independent studies
Provides a precise estimate of the treatment effect, giving due weight to size of different studies included

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2
Q

Definition of heterogeneity

A

The presence of variation in true effect sizes underlying the different studies

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3
Q

Definition of clinical heterogeneity

A

Variation due to participant characteristics, types/timing of outcomes, measurements and intervention characteristics

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4
Q

Definition of statistical heterogeneity

A

Methodology differences between studies

Unknown study characteristics (method of randomization, different controls)

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5
Q

Definition of fixed effect model

A

Assumes 1 true effect size that underlies all studies

All differences in observed effects are due to sampling error

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6
Q

Definition of the random effects model

A

Assumes that the true effect varies from study tp study

Effect size is different due to varying participation of interventions

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7
Q

Definition of data synthesis

A

Combines estimates from selected studies using a fixed effect model or random effects model

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8
Q

Definition of publication bias

A

Bias related to what research is likely to be published among what is available to be published

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9
Q

Definition of tau

A

Compared to the p value, indication of consistency between estimates of effect

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10
Q

Definition of Z

A

The pooled effect that indicates the evidence or lack of for an effect

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11
Q

Where are meta analyses and RCTs in the hierarchy of evidence

A

Meta analyses are the highest level of evidence

RCTs are one level below

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12
Q

What is a meta analysis

A

Combines findings from independent studies and provides a precise estimate of treatment effect
Gives weight to the size of the different studies included

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13
Q

What 3 criteria must be met for a meta analysis to be valid

A

Quality of systematic view
Coverage of all relevant studies
Appropriate methods, considering heterogeneity, bias and sensitivity analysis of main findings

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14
Q

Before undertaking a systematic review, what should you do

A

Check if reviews

  • exist
  • are ongoing

Is a new one justified?

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15
Q

How would you use PICOS to structure your meta analysis

A 
Population
Intervention
Comparator
Outcome
Study design

Used to generate a good research question

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16
Q

What is the protocol and what does it include

A

Document that describes the study conduct
Says what we want to do, must be followed

Includes

  • Objectives (PICOS)
  • Design
  • Method
  • Statistical considerations
  • Methods of dissemination
17
Q

What is heterogeneity and what are the 2 types

A

Presence of variation in true effect sizes underlying different studies
Can differ due to design, patients, interventions and outcomes

  • Clinical heterogeneity
  • Statistical heterogeneity
18
Q

What is clinical and statistical heterogeneity

A

Clinical heterogeneity
-Differences in participant characteristics, types, timing out outcome, measurements and intervention characteristics

Statistical heterogeneity

  • Methodological differences between studies
  • Unknown study characteristics (method of randomization, different controls)
19
Q

How would you assess and measure heterogeneity
Which stats test would you use
What is the degree of freedom
What is the p value

A

Null hypothesis, pooled effect is no different from study effect
x^2 squared used
df=no of studies-1
p-0,05, can be raised for small studies

20
Q

What is the index of heterogeneity

A

% of total variations due to variation between studies

I^2 = 100 x [x^2 - df/x^2]

21
Q

How do you interpret the I2 value and what can it tell you

A

0%, no heterogeneity
25%, low
50%, moderate
75%, high

Can be misleading as inconsistency depends on several factors
Effectiveness may vary, should studies be combined>
Pooled data may not reflect generalizable effectiveness

22
Q

What are the 2 models that help you deal with heterogeneity

A

Fixed effect model

Random effect model

23
Q

What is the fixed effect model
What does it assume
What are the problems when using this model

How do you calculate variance
How do you calculate weight

A

Assumes 1 true effect size that underlies all studies
All differences in observed effects due to sampling error

Open to bias, has narrow CI and may not be appropriate if heterogeneity present

Variance = SE^2
Weight = 1/variance
24
Q

What is the random effects model
What does it assume
What kind of studies are included

How do you calculate variance

A

Assumes that the true effect varies from study to study
Effect size is different due to varying participants, age, intervention

Studies included in analysis assumed to be a random sample of all possible studies that meet inclusion criteria

Variance = SE^2 + intertrial vranke (tau^2)

25
Q

What is publication bias
What is more likely to be published

Why is publication bias a problem

How would you assess publication bias

A

Bias related to what research is likely to be published among what is available to be published

Research with significant findings regardless of quality
By combing only published research => overestimate of effect size

Funnel plots
Effect size against sample size/other indicators of estimate prediction (SE)

26
Q

How would you interpret a funnel plot

A

95% of studies expected to lie within the limit lines
Smaller SE => higher precision

If symmetrical
-Estimates are around the average

If asymmetrical

  • Can show publication bias
  • Or small study effect
27
Q

Describe how the sample size can affect the outcome

When are symmetry tests useful

A

Interventions tested in small studies may differ from those tested in large studies
Symmetry tests exist but aren’t effective when study no is small

28
Q

What are the 5 search strategies for research

A 
Cochrane Register
Conference proceedings
Trial and research registers
Contacted trialists, experts and researchers
Manufacturers of commercial devices

Allows you to check both published and unpublished work

29
Q

What are the 2 types of outcome measure

What is the difference between both of them

A

Primary outcomes

  • outcome that is the most important out of the many outcomes
  • must be defined at the start of the study
  • must also state how the outcome would be measured

Secondary outcomes

  • Planned outcome measure that is not as important but is of interest
  • good to define exactly what be considered a secondary outcome
30
Q

How is the data collected and analysed

A

2 review authors independently select trials for inclusion, assessed trial quality bias risk and extract data
If either one is involved in a study, a 3rd review author handles the data

Trialists contacted for more info
Results analyses as standardized mean difference (SMD) if continuous/risk differences (RD) for dichotomous variables

31
Q

What data is extracted and how is it managed

A

Checklist used to note

  • methods of generating randomization
  • methods of concealment of allocation
  • blinding of assessors
  • ITT
  • AE and dropout reasons
  • participant properties
  • duration of treatment
  • comparison between intervention and controls
32
Q 
Describe how you would use a forest plot in data display
What does 
-Tau
-I2
-Z mean
A

Studies represented by author and pub date

Mean, SD and total no of participants in both control and experimental data

Study results visually and numerically presented

  • bigger square = more meaningful studies with large sample size and smaller CI
  • wider CI => decreased reliability
  • diamond, estimate of pooled effect

Weight of each data set

Tau = tests for consistency between estimates of effect
I2 = proportion of variation in study estimates due to heterogeneity
Z = test for pooled effect
33
Q

What can happen in a subanalysis

A

All data can be split into subgroups according to patient properties and meta analysis performed on subsets

34
Q

What would you include in the conclusion

A

Based on results of pooled data
Results must be interpreted with caution due to heterogeneity
-varying quality
-variation in intensity, duration and treatment
-variation in patient properties

35
Q

What is the purpose of a forest plot

A

Shows heterogeneity/inconsistency between studies

36
Q

How else would you detect heterogeneity sources

A

Sensitivity/subgroup analysis

37
Q

What is the purpose of a funnel plot

A

Detect effect of study size and possible publication bias

38
Q

What sort of studies get more weight

A

Emphasis on RCTs due to fewer biases

Epidemiology and Biostatistics (16 decks)

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