Strength Through Synthesis
Systematic reviews and meta-analyses represent the highest evidence level when executed rigorously. A systematic review comprehensively identifies all published research addressing a specific question, applies predetermined inclusion criteria, assesses methodological quality, and synthesises findings. Meta-analysis statistically combines results, increasing statistical power and detecting patterns invisible in single trials.
PRISMA statement guides systematic review conduct, requiring explicit protocols registered before conducting reviews. The PRISMA flowchart documents identified, included, and excluded studies.
Inclusion/exclusion criteria establish which studies qualify. Stringent criteria ensure methodological quality but may exclude heterogeneous studies. Broad criteria enable broad conclusions but risk combining incomparable studies.
Quality assessment tools evaluate methodological rigor. Fixed effects models assume a single true effect size. Random effects models acknowledge true variation between studies. Heterogeneity describes variation between studies beyond chance. I² statistic quantifies heterogeneity proportion. When studies show markedly different directions, meta-analysis becomes inappropriate.