Systematic reviews and meta analysis

Question 1

what is a systematic review

Answer 1

a review of a clearly formulated question that uses systematic and explicit methods to identify, select, and critically appraise relevant research, and to collect and analyse data from the studies that are included in the review

Question 2

what is a Meta-analysis

Answer 2

refers to statistical techniques used in a systematic review to integrate the results of studies matching the eligibility criteria. combine the published estimates of effect from each study to generate a pooled risk estimate.

Question 3

Why conduct systematic reviews?

Answer 3

Because of the high volume of data that needs to be considered, it’s impossible to evaluate each and every study to synthesise current knowledge. Single studies are often insufficient; poor study design, low numbers, only looks at a subset of the population

Question 4

what are the advantages of a systematic approach

Answer 4

Transparent process because of the explicit methods in identifying and rejecting studies. A meta-analysis, if appropriate, will increase the power of the study and enhance the precision of estimates of treatment effects, accounting for sample size, and uncertainties. Systematic reviews may demonstrate the lack of adequate evidence and thus identify areas where further studies are needed.

Question 5

what is stage I of a systematic review

Answer 5

Planning the review - Clearly define the research question to be addressed

Question 6

what is stage II of a systematic review

Answer 6

Identification of research - Clearly defined search criteria to include all published literature and exhaustive searches. Selection of Studies - Inclusion and exclusion criteria (i.e. based on study design and quality, year, sample size, completeness etc). Study quality assessment – Quality assessed based on recognised or user defined criteria (e.g selection/measurement bias, methodological quality, follow-up/completeness etc)

Question 7

what is stage III of a systematic review

Answer 7

Reporting and dissemination – Study details need to be abstracted and details tabulated to show summary of the findings. We can estimate an overall effect by combining the data in a Meta-analysis

Question 8

what are the strengths of meta analyses

Answer 8

More subjects can be included than any single constituent study, producing a more reliable and precise estimate of effect. Differences (heterogeneity) between published studies can be identified and explored

Question 9

what are the limitations of meta analyses

Answer 9

If the studies are too heterogeneous, it may be inappropriate, even misleading to statistically pool the results from separate studies.

Question 10

why are the effects of each individual study pooled in a meta analyses

Answer 10

to produce a weighted average effect across all studies.

Question 11

what is the most common way of presenting the results from a meta-analysis

Answer 11

using a forest plot. this is a graphical representation of the results from each study included in a systematic review, together with the combined meta-analysis result

Question 12

describe a forest plot

Answer 12

Each study is represented by a box and line – the size of the box corresponds to the weight given to that individual study; the horizontal lines correspond to the 95% confidence interval.The overall estimate from the meta-analysis is usually shown as a diamond at the bottom of the plot. The centre of the diamond and dashed line corresponds to the
summary effect estimate; the width of the diamond represents the confidence interval around this estimate.

Question 13

what are the potential biases and limitations of meta analyses and systematic reviews

Answer 13

Inconsistency of results. Low study quality. Hetrogenity. Null or non-significant findings are less likely to be reported/ published than statistically significant findings
Thisbiasmay distort meta-analyses and systematic reviews

Question 14

what is publication bias

Answer 14

refers to the greater likelihood of research with statistically significant results to be published in the peerreviewed literature in comparison to those with null or nonsignificant results.

Question 15

what can publication bias result in in meta analyses

Answer 15

Failure to include all relevant data in a meta-analysis may mean the effect of an intervention/exposure is over- or under-estimated.

Question 16

how can publication bias in meta-analyses be explored

Answer 16

by using funnel plots Funnel plots, which show whether there is a link between study size (or precision) and the effect estimate

Question 17

what is heterogeneity

Answer 17

Studies that are trying to answer the same question may still differ with respect to the exact population, interventions/ exposure, outcomes and designs used. Even where these factors are homogeneous, heterogeneity may still exist because of clinical differences, methodological differences or unknown study characteristics.

Question 18

how can heterogeneity be explored

Answer 18

using Galbraith (radial) plots.

Question 19

what are the limitations in conducting systematic reviews

Answer 19

there are too few studies matching the eligibility criteria defined, a systematic review might not add much to the field. If the methodological quality of studies is inadequate, then the findings of reviews of this material may also be compromised.