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.HEALTH&SOCIETY Y4 > CAT: SYSTEMATIC REVIEW > Flashcards

CAT: SYSTEMATIC REVIEW Flashcards

1
Q

Pros of systematic reviews?

A

Brings together all of the best available evidence for a question
Allows recognition of important treatment effects by combining the results of small trials that individually might have lacked the power to consistently demonstrate differences among treatments
Explicit methods which limit bias in identifying and rejecting studies so conclusions are more reliable and accurate
Large amounts of infromation can be assimilated quickly by healthcare providers, researchers and policy makers
Reasons for heterogeneity can be identified and new hypotheses can be generated about particular subgroups
They have more statistical power than individual studies
Utilises results from RCTs which are the best evidence
Recognised as the strongest design
They can make a meta-analysis to increase the precision of the overall results

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2
Q

Cons of systematic reviews?

A

Reporting quality varies
Poor external validity
High risk of publication bias
Time and resource intensive
Important data can often be overlooked e.g. grey literature

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3
Q

What is the difference between dichotomous and continuous data?

A

Dichotomous data is where each outcome is one of only two possible categorical responses
Continuous data can take any value

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4
Q

How can dichotomous results be expressed?

A

Relative risk (RR)
Odds ratio
Risk different
ARR/NNT

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5
Q

How can continuous results be expressed?

A

Mean difference or standardised mean difference

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6
Q

What is clinical heterogeneity?

A

differences in the characteristics of the study with respect to population, intervention or outcomes
In exam practice it said “forms of treatment varied between individual groups”

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7
Q

What is statistical heterogeneity?

A

variability in estimates of treatment effectiveness when examining a similar outcome or measuring the same effect in multiple studies.

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8
Q

What is a meta-analysis?

A

When the results of more than 1 study are pooled statistically to create a summary estimate of treatment effectiveness to give a more precise estimate of how well a treatment works than any individual trial

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9
Q

Why are RCTs used for systematic reviews involving therapy?

A

Less susceptible to selection and information bias so considered the most robust and reliable

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10
Q

What is publication bias?

A

Failure to publish the results of a study on the basis of issues other than the quality of the study e.g. based on the nature and strength of the findings

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11
Q

What is language bias?

A

Studies with positive findings are more likely to be published in an England language journal and also more quickly than studies with inconclusive or negative findings
So a thorough SR should not restrict itself to journals written in English

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12
Q

How should studies/data be reviewed in a systematic review?

A

By at least 2 reviewers working independantly from each other and any differences should be settled by consensus or by a third person

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13
Q

What are the 2 statistical models to combine results for a meta analysis?

A

Random effects model
Fixed effects model

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14
Q

How can the robustness of a meta-analysis be tested?

A

By a sensitivity analysis

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15
Q

What is the random effects model?

A

This model assumes that thr studies are estimating different effects due to random error i.,e. Chance but ALSO due to heterogeneity which is always present
This is used when there is substantial heterogeneity among studies

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16
Q

What is the fixed effects model?

A

This model assumes all studies are estimating the same underlying effect and variability amongst the studies is just due to random error i.e. Chance. It does not recognise any heterogeneity
This model is used with heterogeneity is low!

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17
Q

What is impprtant about selecting relevant studies for systematic reviews?

A

Multiple data bases should be used - cochrane, medline, embase
Include unpublished studies, non-English studies, grey literature, made personal contact with experts, raw data from published trials
Reviewing reference lists of included studies
Give clear examples of search terms, sources searched and the retrieval process
They should have a prisma/flow diagram

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18
Q

What should the authors do to assess quality of included studies in a systematic review?

A

Each trial should be evaluated in terms sof its methodological quality, precision and external validity
Methodological quality - is there likely to be bias?
Precision - is there a measure of likelihood of random errors i.e. confidence interval width
External validity - how generalisable are the results

using a checklist for this can increase the replicability - this is super important!!!

Quality criteria commonly used for RCTs includes: concealed, random allocation; groups with similar known prognostic factors; equal treatment of groups; ITT analysis

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19
Q

what is selection bias?

A

Systematic differences between baseline characteristics of the groups that are compared due to proper randomisation not being achieved. This means the sample is not representative

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20
Q

What is internal validity?

A

The extent to which the observed results represent the truth in the population being studied i.e. free from bias. It’s the degree of confidence that the causal relationship you are testing is not influenced by other factors or variables.

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21
Q

What is external validity?

A

The extent to which you can generalise the findings of a study to other situations, people, settings and measures

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22
Q

What is performance bias?

A

Systematic differences that occur due to knowledge of interventions allocation, in either the researcher or the participant
Effective blinding reduces this

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23
Q

What is detection bias?

A

systematic differences between groups in methods for detecting outcomes
E.g, 1 group is screened more regularly

Aka ascertainment and observer bias

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24
Q

What is attrition bias?

A

Systematic differences between study groups in the number and way participants are lost from a study

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25
Q

What is reporting bias?

A

a type of bias that occurs when certain results, outcomes, or information are selectively reported or highlighted, while others are suppressed or underreported.

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26
Q

When can a meta-analysis not be done?

A

If studies are too heterogeneous
If studies have too high a risk of bias e.g. publication
If studies are too low a quality or there is not enough data from a study
If there’s a limited number of studies

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27
Q

What is homogeneity?
What will be seen on a forest plot?

A

When the results of each individual trial are compatable with the results of others
On a forest plot all of the confidence intervals would overlap

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28
Q

How can you assess heterogeneity in studies?

A

Cochran’s Q test - which is based off the chi-squared test (X^2)
I^2 statistic
Eyeball test - looking for overlap of CI of trials with the summary estimate
L’Abbe plots

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29
Q

How can you investigate for cause of heterogeneity?

A

Subgroup analysis
Meta-regression

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30
Q

What is the line of no effect on a forest plot?

A

This corresponds to the value of 1 for the binary outcome i.e. the risk ratio
This is the position at which there is no clear difference between the intervention and control group

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31
Q

What is a standardised mean difference?

A

A summary statistic in meta-analysis when the studies all assess the same outcome but measure it in a variety of ways (for example, all studies measure depression but they use different psychometric scales).
So it is necessary to standardize the results of the studies to a uniform scale before they can be combined. The standardized mean difference expresses the size of the intervention effect in each study relative to the variability observed in that study.

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32
Q

What is I squared? How do we interpret it?

A

This is a measure of the % of variation in effect sizes between studies due to heterogeneity rather than chance
Anything over 25% consider as high!!

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33
Q

What is a subgroup analysis?

A

When all participants data included in the meta analysis is split into subgroups according to the characteristics of pts and a meta analysis is performed on the sub set
This can investigate heterogeneous results or answer specific questions about a particular characteristic

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34
Q

What is a sensitivity analysis?

A

A form of subgroup analysis done by quality of the individual studies

systematically varying different elements of the review process to observe how sensitive the overall results are to this change.
If the conclusion results remain consistent across different scenarios then it adds strength to the reliability of the findings and suggests robustness

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35
Q

Advantages of a meta-analysis?

A

Improves precision by increase the sample size
Allows for objective appraisal of evidence
Heterogeneity between study results can be explained
Increases the generalizability
Answers questions not posed by individual studies
Establishes questions for future RCTs
Reduces time and energy decision-makers spend looking at research

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36
Q

What is a systematic review?

A

A review that summarises the evidence on a clearly formulated review question according to a predefined protocol, using systematic and explicit/transparent/reproducible methods to identify, select and appraise relevant studies, and to extract, analyse, collate and report their findings.

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37
Q

What does it mean if, on a forest plot, the horizontal line of a trial does not cross the line of no effect?

A

There is a 95% chance that there is a real difference between the groups

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38
Q

What does it mean if, on a forest plot, the horizontal line of a trial does cross the line of no effect?

A

Either there is no significant difference between the treatments or that the sample size was too small to allow us to be confident where the true result lies

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39
Q

Outline why a systematic review of RCTs is an appropriate match to a clinical question on treatment effectiveness?

A

RCTs are an appropriate match for treatment effectivenes because it reduces bias via randomisation which allows for exmination of cause-effect relationships between an intervention and outcome
Systematic reviews bring together the best available evidence and may allow greater precision in estimating effectiveness if combined with a meta-analysis

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40
Q

Why is intention to treat analysis important?

A

The intention-to-treat analysis preserves the prognostic balance afforded by randomization, thereby minimizing any risk of bias. important for preventing attrition bias

they also mirror actual practice, when not everyone adheres to the treatment, and the treatment people have may be changed according to how their condition responds to it.

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41
Q

What do you get marks for when in the exam they ask you to explain a forest plot?

A

Outline that the figure shows e.g. figure 2 shows the results of a pooled analysis of 7 RCTs
Identifying individual effect and confidence intervals for each study e.g. results are expressed in terms of whether treatment was associated with an increased rate of xyz… 95% confidence intervals are presented for each study and these represent…
Identifying the null effect and say how it represents the RR of 1 so no association between different interventions
Identifying and correctly interpreting the overall summary
Heterogeneity or weighting

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42
Q

Examples for answering: what other outcomes would you like to see in studies?

A

Patient outcome measures
Side effects of drugs
Quality of life
Patient acceptibility/satisfaction

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43
Q

What is GRADE?

A

Grading of Recommendations, Assessment, Development, and Evaluations
A systematic approach to rate the certainty of evidence in systematic reviews and other evidence syntheses

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44
Q

What is methodological heterogeneity?

A

variability in study design and quality across different studies investigating a similar topic

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45
Q

In systematic reviews, why are outcomes generally not used as part of the eligibility criteria for including studies?

A

As systematic reviews aim to include all rigorous studies of a particular comparison of interventions in a particular population of participants, regardless of the outcomes measured or reported.

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46
Q

Why might a systematic review avoid using newer diagnostic criteria for defining diseases or conditions of interest?

A

Newer diagnostic criteria might not have been used in earlier studies, leading to the exclusion of valuable data.

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47
Q

What are examples of inactive control interventions, and how do they differ from active control interventions?

A

Inactive control interventions include placebo, no treatment, standard care, or a waiting list control. They differ from active control interventions, which involve an active element, such as a different variant of the same intervention, a different drug, or a different kind of therapy.

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48
Q

Why is it important to consider variation in the intervention in a systematic review?

A

As significant differences in dosage/intensity, mode of delivery, frequency, or duration can lead to substantially different effects on the participants and outcomes of interest. This could affect theinternal validity and reliability of the review’s results, so it might be necessary to restrict the variation to ensure consistency across the included studies.

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49
Q

Why is it essential to consider both adverse effects and beneficial effects in a systematic review’s outcome assessment?

A

It is crucial to assess both adverse and beneficial effects to ensure a balanced and comprehensive understanding of the intervention’s impact. This helps in determining the overall risk-benefit ratio and informs clinical decision-making.

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50
Q

What differentiates primary outcomes from secondary outcomes in a systematic review?

A

Primary outcomes are the key focus of the review and form the basis for major conclusions about the intervention’s effects. Secondary outcomes are those that aren’t chosen as primary outcomes but still provide important additional insights. They may include outcomes specific to certain comparisons or additional outcomes that the review intends to address, such as surrogate measures or laboratory tests.

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51
Q

How does publication bias impact meta analysis findings?

A

Abstracts reporting insignificant findings are excluded so there will be an overestimation of the effects = reduces the internal validity
Reduces the number of studies so will reduce the power of the study

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52
Q

Name some methods used in systematic reviews to check for the existence of publication bias?

A

Funnel plots
Egger regression test
Fail Safe sample size
Begg-Mazumdar’s test
Cumulative meta analysis

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53
Q

In a systematic review, what condition must be met before individual study results can be combined in a meta-analysis?

A

There must be a reasonable degree of homogeneity among thr studies

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54
Q

Examples of groups of outcomes in a study

A

patient outcomes
clinical outcomes
HRQoL outcomes
health economics

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55
Q

What is Egger’s test?

A

A statistical method to detect publication bias
Uses linear regression to detect assymetry in a funnel plot!

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56
Q

What is important about the specific search strategy in systematic reviews?

A

There should be a clear search strategy with a description of the approach to searching
There should be evidence of a wide range of logical and relevant keywords and terms
There should be evidence that subject headings and indexing terms were used
Any limits on the search should be described and their potential impact explained e.g. dates, language

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57
Q

What is important about study eligibility in a systematic review?

A

The review should have pre-defined objectives and eligibility criteria
Is there were any restrictions on the eligibility criteria, were they appropriate?
Did the types of included studies match the review question?

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58
Q

When should the literature search for a systematic review be done?

A

Within 24 months of completion of the review

59
Q

What are the “essential features of a systematic review”?

A

Clear objectives
A methodological approach that is transparent and replicable
Explicit criteria for study selection to identify all the relevant studies
Assessment of the quality of included studies such as assessing bias
Consideration of which studies to combine

60
Q

Why can’t you just perform a quick MEDLINE search for a systematic review?

A

Complex and sensitive search strategies are needed to identify all potential trials
Some clinical trials will be missed if they are published in a journal not listed by MEDLINE

61
Q

What is the Cochrane Controlled Trials Registry?

A

The largest and most complete database of clinical trials in the world
It is huge and sets very high standards for the reviews it publishes

62
Q

How can you prevent language bias?

A

Include a search for high quality unpublished trials
Dont restrict yourself to journals written in English

63
Q

When do funnel plots have limited value in a systematic review?

A

When there are less than 10 RCTs included

64
Q

What is the Number Needed To Treat?

A

The number of pts one would need to treat to achieve 1 additional cure

65
Q

What is the point estimate?

A

Calculating a single value which is the best estimate of the treatment effect

66
Q

Is the fixed efefcts model or the random effects model more likely to show statistically significant results?

A

The fixed effect models

67
Q

When should random and fixed effects models give similar results?

A

When the combined studies have statistically homogeneity

68
Q

What is PRISMA?

A

Preferred Reporting Items for Systematic Rewiews and Meta-Analyses
A set of guidelines designed to improve the reporting of systematic reviews and meta-analyses in healthcare research

69
Q

Why is it important for systematic reviews to include a PRISMA flow diagram?

A

It visually represents the process of study selection. This allows reviewers to spot potential selection bias
This ensures transparency and reproducibility of a systematic review

70
Q

Advantages of using a SR over primary data studies?

A

Speed - why conduct a new RCT if answer is already available in published research
Ethics - is it defensible to conduct a controlled trial if answer is already available
Statistical power increased and more precision of estimates

71
Q

What is CINAHL?

A

Cumulative Index to Nursing and Allied Health Literature

72
Q

How can inclusion bias occur in systematic reviews?

A

Inclusion and exclusion criteria can be set to favour studies with certain outcomes which can produce systematic differences

73
Q

Outline the structure of a funnel plot?

A

Each dot in the plot represents an individual study.
X-axis = log of odds ratio (effect size of Tx)
Y-axis = standard error (represents study precision so the larger the study the higher up it will be!)
The vertical dotted line is the overall effect
The diagonal dotted lines represent the 95% confidence intervals

74
Q

Describe how to interpret funnel plots?

A

Effect estimates from small studies will therefore scatter more widely at the bottom of the graph, with the spread narrowing among larger studies.
In the absence of bias the plot should approximately resemble a symmetrical inverted funnel. If there is bias this will be asymmetrical

75
Q

What is a L’Abbe plot?

A

Plots the event rate in intervention group against event rate in control group
Aims to explore heterogeneity of effect estimates within a meta-analysis

76
Q

What method is used to combine the results of multiple studies?

A

Mantel-Haenszel procedure

77
Q

what are MeSH terms?

A

Medical Subject Headings - controlled terms used in the MEDLINE database to index citations

78
Q

what is the Cochrane Collaboration?

A

an international collaboration that aims to help with informed decision-making on healthcare topics by preparing, maintaining and ensuring accesability of systematic reviews on interventions

79
Q

sytematic vs random error

A

random error = a chance difference between the observed and true values of something (e.g., a researcher misreading a weighing scale records an incorrect measurement).
systematic error = A consistent or proportional difference between the observed and true values of something (e.g. scales being miscalibrated)

80
Q

what is the power of a study?

A

the ability of a test to statistically demonstrate a difference when one exists
when a test has a low power, a large sample size is required otherwise there is a risk that a possible difference may be missed

81
Q

what does the quality of a study depend on?

A

the degree to which its design, conduct and analysis minimises bias

82
Q
A
83
Q

What is a forest plot?

A

A graphic display of the individual effects observed in individual studies included in a SR against some measure of study information
Used for exploration for rush if publication bias

84
Q

What is meta-regression?

A

a type of meta-analysis that allows you to explore how various study-level characteristics (like study design, participant characteristics, or intervention details) might influence the overall effect size.
A multi variable model with effect estimates of individual studies as dependant variables and various study characteristics as independent variables

85
Q

What is sampling bias?

A

A type of selection bias when some members of the intended population are less likely to be included than others
I.e. the study isn’t representative of the whole population.
The skewed sample could lead to a misrepresentation of the data and flawed conclusions.

86
Q

What is treatment fidelity?

A

How accurately the intervention is reproduced from the protocol
I.e. it refers to the extent to which an intervention is implemented as planned.

87
Q

What is a spurious association?

A

When an association has risen by chance and is not real

88
Q

What is an indirect association?

A

When the association is due to the presence of another factor i.e. a confounding variable

89
Q

What is face validity?

A

The general impression of a test
Does it appear to test what it is meant to

90
Q

What is content validity?

A

The extent to which a test or measure assesses the full content of a subject

91
Q

What is criterion validity?

A

This concerns the comparison of testes
Comparing a new test to see if it works as well as an old, accepted method

92
Q

What is concurrent criterion validity?

A

The predictor and criterion data are collected at or about the same time

93
Q

What is predictive criterion validity?

A

The predictor scores are collected first and the criterion data are collected at some later point
This is when you want to know if a test predicts future outcomes

94
Q

What is construct validity?

A

The extent to which a test measures the construct it aims to

95
Q

What is convergent validity?

A

When a test has a high correlation with another test that measures the same construct

96
Q

What is divergent validity?

A

When a test has low correlation with a test that measures a different construct

97
Q

What is a p value?

A

The probability given H0 that the observed effects or more extreme effects in a study could have occurred due to chance

98
Q

What is the Pearson correlation coefficient for?

A

the most common way of measuring a linear correlation.
It is a number between –1 and 1 that measures the strength and direction of the relationship between two variables.

99
Q

1SD from the mean is what %?

A

68.3

100
Q

2SD from the mean is what %?

A

95.4%

101
Q

3SD from the mean is what %?

A

99.7%

102
Q

What is margin of error?

A

a statistic expressing the amount of random sampling error in the results of a survey.
The larger the margin of error, the less confidence one should have that a poll result would reflect the result of a census of the entire population.

103
Q

What is standard error of the mean>

A

The measure of how far the sample mean of the data is likely to be from the true population mean

104
Q

How do you calculate SEM?

A

SD/ square root of no of patients

105
Q

What is a histogram?

A

A graphical display of continuous data where the values have been categorised into a number of categories

106
Q

What is a scatter plot?

A

Graphical representation using Cartesian coordinates to display values for two variables for a set of data

107
Q

Best study design for a question on therapy?

A

RCT>cohort>case control

108
Q

Best study design for a question on prognosis?

A

Cohort study > case control > case series

109
Q

Best study design for a question on prevention?

A

RCT>cohort>case control

110
Q

Best study design for a question on diagnostic test?

A

A specific type of cross-sectional study called : Prospective blind comparison to gold standard

111
Q

Best study design for a question on aetiology?

A

RCT>cohort>Case control
(Although it’s not always ethical to randomise people to a known harmful exposure!!)

112
Q

How do you interpret Egger’s test?

A

P <0.05 suggests publication bias

113
Q

What is citation bias?

A

when authors preferentially cite research that supports their own findings or claims, or research that showed what they had hoped to find but didn’t find in their research

114
Q

What is survivorship bias?

A

a type of selection bias that ignores the unsuccessful outcomes of a selection process

115
Q

What is non-response bias?

A

When people who refuse to participate or drop out systematically differ from those who take part

116
Q

What is undercoverage bias?

A

When some members of the population are inadequately represented in the sample

117
Q

What is evidence selection bias?

A

This occurs when a systematic review does not identify all the available data on a topic

118
Q

How can evidence selection bias arise within a systematic review?

A

It can arise from publication bias, where data from statistically significant studies are more likely to be published than those that are not statistically significant
It can arise from poor search strategies
It can arise from when there is unconscious selection of preferred studies

119
Q

How can authors address evidence selection bias?

A

Have 1 reviewer to extract data and another reviewer to check for accuracy

120
Q

What is time lag bias?

A

Where studies with unfavourable findings take longer to be published

121
Q

What is selective outcome reporting?

A

Where non-significant study outcomes are entirely excluded on publication

122
Q

What is availability bias?

A

When you rely disproportionately upon the most readily available data

123
Q

What is reviewer selection bias?

A

This can occur if reviewers deliberately seek only individual participant data from a subset of existing studies and this subset does not reflect thr entire evidence base

124
Q

What is a crossover study?

A

A type of clinical trial in which all participants receive the same two or more treatments, but the order in which they receive them depends on the group to which they are randomly assigned.
E.g. AB/BA study!

125
Q

What is a factorial trial?

A

When 2 or more intervention comparisons are carried out simultaneously
E.g. participants may be randomized to receive aspirin or placebo, and also randomized to receive a behavioural intervention or standard care

126
Q

What is the healthy entrant effect? what causes it?

A

The tendency for participants in studies included in the review to be healthier or have better outcomes compared to the general population = shows reductions in mortality rates
occurs due to strict inclusion criteria, drop out rates and selecction bias

127
Q

What is a cluster-randomised trials?

A

In cluster-randomized trials, groups of individuals (e.g. schools) rather than individuals are randomized to different interventions
E.g. may be used to evaluate the group effect of an intervention such as herd immunity of a vaccine

128
Q

Accuracy vs precision!!!

A

Accuracy refers to how close a measurement is to the true or accepted value. Precision refers to how close measurements of the same item are to each other

129
Q

What is non-differential error?

A

Random misclassification of exposure that is equal in both groups - leads to a bias towards H0

130
Q

What is differential error?

A

Non-random misclassification of exposure causing bias in either direction = creates spurious associations or obscures ones

131
Q

What should you discuss in the final discussion of a systematic review i..e the applicability?

A

Make a final statement about whether or not you want to apply this to your pt population

Discuss:
- biases
- costs
- adverse events
- information on pt preferences
- any issues with the study e.g. heterogeneity, power, sensitivity analysis
- differences in your population

132
Q

How do you calculate a relative risk reduction?

A

100% x (1- relative risk)
E.g. a risk ratio of 0.75 translates to a RRR of 25%

RRR = (CER - EER)/CER.

133
Q

Which study type expresses results as odds ratios?

A

Case control studies

134
Q

What is observer bias?

A

When the assessors of the outcome know the group assignment and have expectations for the outcomes

135
Q

What is PROSPEROUS?

A

The International Prospective Register of Systematic Reviews
An online database of systematic review protocols

136
Q

Examples of risk of bias tools?

A

RoB2 (Risk of Bias 2)
Cochrane risk of bias tool
Newcastle-Ottawa scale
GRADE

137
Q

What is funding bias?

A

the tendency of a scientific study to support the interests of the study’s financial sponsor

138
Q

what are some ways proposed to prevent publication bias?

A

creation of study registers
advance publication of research design

139
Q

definition of a 95% confidence interval

A

a range within which we can be 95% certain that the true effect lies

140
Q

what is ordinal data?

A

where each individual’s outcome is one of several ordered categories, or generated by scoring and summing categorical responses;

141
Q

what is a risk ratio?

A

aka the relative risk
the ratio of the risk of an event for the exposure group to the risk for the non-exposure group

142
Q

what is an Odds ratio?

A

the odds that an outcome will occur given a particular exposure, compared to the odds of the outcome occurring in the absence of that exposure.
it quantifies the strength of the association between 2 events, A and B

143
Q

what does the size of a black square for each study on a forest plot represent?

A

the weight of the study in that meta analysis

144
Q

4 ways to address confounding?

A

restriction
mathcing
stratification
multiple variable regression

.HEALTH&SOCIETY Y4 (17 decks)

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