make notes on “systematic review and meta analysis each” for md derma

make notes on “systematic review and meta analysis each” for md derma theory exam, make it short and crisp yet readable and to be able to write an answer

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Cochrane systematic review meta-analysis handbook PRISMA 2020

Systematic Review

Definition:
A systematic review is a structured, transparent and reproducible review of all relevant studies addressing a focused clinical question. It uses predefined methods to identify, select, critically appraise and synthesize evidence.

Purpose:
To provide the best available summary of evidence for clinical decision-making, guidelines and research planning.

Steps in a Systematic Review

Frame a focused question using PICO:
- Population
- Intervention/exposure
- Comparator
- Outcome
Prepare a protocol
Define objectives, eligibility criteria, databases, outcomes and analysis plan. Ideally register it in PROSPERO.
Comprehensive literature search
Search databases such as PubMed/MEDLINE, Embase, Cochrane Library, trial registries and reference lists.
Study selection
Screen titles/abstracts, then full texts according to predefined inclusion and exclusion criteria. This is shown by a PRISMA flow diagram.
Data extraction
Extract study characteristics, participants, interventions, outcomes and results using a standardized form.
Assess risk of bias / study quality
Examples: RoB 2 for randomized controlled trials, ROBINS-I for non-randomized studies.
Evidence synthesis
Results may be synthesized narratively or statistically by meta-analysis, if studies are sufficiently comparable.
Interpretation and reporting
Discuss certainty of evidence, limitations, clinical relevance and applicability. Report using PRISMA 2020.

Advantages

Provides an organized summary of all available evidence.
Reduces selective citation and reviewer bias.
Helps resolve conflicting study results.
Identifies gaps in evidence.
Usually placed high in the evidence hierarchy when based on good-quality studies.

Limitations

Quality depends on the quality of included studies: “garbage in, garbage out.”
May be affected by publication bias.
Time-consuming and methodologically demanding.
Heterogeneous studies may prevent meaningful pooling.
A systematic review is not necessarily a meta-analysis.

Meta-analysis

Definition:
Meta-analysis is a statistical technique that combines numerical results from two or more sufficiently similar studies to generate a pooled estimate of effect.

Key point:
It is often a component of a systematic review, but a systematic review can be done without meta-analysis.

Requirements before Meta-analysis

Similar clinical question and population.
Comparable interventions/exposures and outcomes.
Adequate methodological similarity.
Sufficient data from included studies.

Effect Measures

Dichotomous outcomes: Risk ratio (RR), odds ratio (OR), risk difference (RD).
Continuous outcomes: Mean difference (MD) or standardized mean difference (SMD).
Time-to-event outcomes: Hazard ratio (HR).

Models of Meta-analysis

Fixed-effect model
Assumes all studies estimate one true common effect. Used when heterogeneity is minimal.
Random-effects model
Assumes true effects vary across studies. More appropriate when clinical or statistical heterogeneity exists.

Forest Plot

A forest plot graphically displays:

Effect estimate of each study, shown as a square.
Confidence interval, shown as a horizontal line.
Pooled effect, shown as a diamond.
Vertical line of no effect: RR/OR = 1; MD = 0.

Heterogeneity

Heterogeneity means variation in study results.

Assessment:

Chi-square (Q) test
I² statistic: percentage of variation due to heterogeneity rather than chance.
- 0%-40%: may be unimportant
- 30%-60%: moderate
- 50%-90%: substantial
- 75%-100%: considerable

Management: check clinical and methodological differences, perform subgroup or sensitivity analysis, or avoid pooling studies.

Publication Bias

Studies with positive findings are more likely to be published. It can be assessed using a funnel plot. An asymmetric funnel plot suggests possible publication bias, though heterogeneity can also cause asymmetry.

Advantages

Increases total sample size and statistical power.
Gives a more precise pooled effect estimate.
Can detect small but clinically relevant effects.
Allows exploration of heterogeneity and subgroups.

Limitations

Inappropriate pooling can give misleading results.
Influenced by poor-quality primary studies.
Heterogeneity may limit validity.
Subject to publication bias and selective outcome reporting.
Statistical significance does not always imply clinical significance.

Difference Between Systematic Review and Meta-analysis

Feature	Systematic review	Meta-analysis
Nature	Structured review of evidence	Statistical pooling of results
Main aim	Identify, appraise and synthesize all relevant studies	Estimate a combined effect size
Statistical analysis	Not compulsory	Essential
Output	Qualitative and/or quantitative evidence synthesis	Pooled numerical estimate, forest plot
Relationship	Can exist alone	Usually conducted within a systematic review

Conclusion: A well-conducted systematic review answers a focused question through transparent methods. Meta-analysis, when appropriate, strengthens it by providing a pooled quantitative estimate. PRISMA is a reporting guideline, not proof that the review itself was methodologically sound, as clarified by the PRISMA guidance and Cochrane reporting guidance.

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