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CPH PPD 2 > META-ANALYSIS > Flashcards

META-ANALYSIS Flashcards

1
Q

What is a systematic review?

A

Impartial summary of existing research to aid doctors on decisions of effectiveness

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2
Q

Advantages of systematic review

A

You don’t have to spend a heap of money to do a ‘new amazing study’, but instead can analyse a bunch of smaller studies

They are methodical and objective

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3
Q

What does the validity of a systematic review depend on?

A

Quality of evidence or research which is included
Needs to be unbiased
Randomisation, blinding can improve validity

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4
Q

Aims of a systematic review

A

Results from a large number of studies are refined and reduced to manageable quantity

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5
Q

Comment on the precision in systematic reviews

A

Quantitative systematic review combines results across all studies. By doing so the number of subjects for which overall total effect is calculated is combined, thereby providing estimates with increased precision

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6
Q

Comment on efficiency of systematic reviews

A

Quicker and less costly than undertaking new study. May prevent need for further studies

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7
Q

Common on the generalisability of a systematic review

A

Results can be generalised to a wider patient population.

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8
Q

What is a meta-analysis?

A

Systematic review providing quantitative (statistical) estimate(s) of effectiveness:
• Combines results independent studies

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9
Q

Advantage of meta-analysis

A

Reduces evidence into single estimate(s)

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10
Q

List 4 advantages of a meta-analysis vs single study

A
  1. Accumulates evidence and reduces it to manageable size
  2. Single estimate will have increased precision compared to original studies on their own as estimate is derived from many different studies
  3. This reduces sampling error
  4. Overall estimate can suggest efficacy of effectiveness of treatment that was not seen in a single study
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11
Q

List 5 disadvantages of meta-analysis

A

Prone to bias as MORE LIKELY TO BE:

  1. Published (publication bias)
  2. Published rapidly (time lag bias)
  3. Published in English (language bias)
  4. Published more than once (multiple publication bias)
  5. Cited by others (citation bias)
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12
Q

Why would you want to carry out a systematic review instead of individually looking at the studies seperately?

A

For treatment of a particular health condition literature will typically contain numerous studies. As such it might be difficult to accumulate all evidence and assess effectiveness of particular treatment objectively, not least since studies may contradict or be inconclusive. To this end, systematic reviews are used to accumulate evidence and provide a balanced summary enabling decision making. It collects and reduces results from across all relevant studies, either published or otherwise, for same or similar treatments

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13
Q

RR >1.0 favours what?

A

Control

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14
Q

RR <1.0 favours what?

A

Intervention

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15
Q

What does a forest plot show?

A

A way of showing the outcomes from a multitude of trials. The dots in the middle vary in size depending on how big sample size for the study was. In addition to that there is a diamond at bottom for each drug which shows the overall result for each

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16
Q

If it crosses the midpoint of a forest plot, what does this favour?

A

Control

17
Q

The smaller the horizontal line the _____

A

Better

18
Q

The bigger the dot the more valuable that study is in the analysis - why?

A

Sample size was bigger

19
Q

What is a forest plot?

A

Graphical representation of the results of a meta-analyses

20
Q

What is the solid vertical line in the centre of a forest plot graph?

A

“Line of no effect” - that is, a relative risk (risk ratio) of 1.0, representing no difference in risk between intervention and control groups

21
Q

Relative risk in intervention = what does the figure mean

A

RR <1.0 implies that risk of adverse outcome was reduced with intervention relative to control treatment, whereas RR >1.0 implies risk was increased with intervention

22
Q

The amount that each trial contributed is indicated under the heading “Weight (%).” The percentage weight contributed by a trial is determined by what?

A

Precision of its sample estimate for population parameter. Trials with more precise estimates, as indicated by those with narrower confidence intervals, had a greater weight

23
Q

What does a test of heterogeneity assess?

A

Assesses extent of variation between sample estimates in a meta-analysis

24
Q

How is heterogeneity tested?

A

Performed in a similar way to traditional statistical hypothesis testing, being a null + alternative hypothesis. Null = statistical homogeneity exists - that is, sample RRs are of similar magnitude, and variation between them is no more than would be expected when taking samples from same population. Alternative hypothesis = statistical heterogeneity is present, and sample estimates differ substantially

25
Q

What might heterogeneity sugget?

A

Effects of treatment differ between subgroups (such as ethnic groups) in population

26
Q

The results of a statistical test of heterogeneity a meta-analysis are as follows: χ2=3.62, df=5, P=0.60, I2=0%.
Interpret

A

P = 0.60, indicating there was no evidence to reject null hypothesis in favour of alternative. Therefore, homogeneity exists between the sample estimates

χ2 is test statistic resulting from statistical test used to derive P value. The value for degrees of freedom (“df”) equals the number of trials minus one and is used along with the test statistic to calculate the P value.

Higgins I2 statistic, simply referred to as I2 = 0%, which corroborates inference from statistical test of the hypotheses that statistical homogeneity exists

27
Q

Describe the Higgins I2 statistic, simply referred to as I2

A

Used as an alternative test for heterogeneity. Represents percentage of variation between sample estimates that is due to heterogeneity. Can take values from 0% to 100%, with 0% indicating statistical homogeneity. Significant statistical heterogeneity is often considered to be present >50%

28
Q

What is intention to treat?

A

Once randomised, always analysed in that group

29
Q

What is per protocol?

A

Per-protocol (PP) analysis refers to inclusion in analysis of only those patients who strictly adhered to protocol

30
Q

What is as treated analysis?

A

Term “as treated” means that in analysis/summaries, treatment assignment is based on actual treatment patients receive, not treatment patients are supposed to receive

31
Q

Why should you always use intention to treat analysis?

A

PRESERVES RANDOMISATION. Intent-to-treat (ITT) analyses in superiority trials protect against kinds of bias that might be associated with early departure from study

CPH PPD 2 (11 decks)

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