heterogeneity-investigation

name	heterogeneity-investigation
description	Explain why different studies reach different conclusions — heterogeneity investigation protocol. Budget: 30 studies, 30 effect sizes, 50 web searches.

Heterogeneity Investigation Strategy

Design a protocol to investigate and explain between-study heterogeneity — why studies of the same question reach different conclusions.

Purpose

When a meta-analysis reveals substantial heterogeneity (I2 > 50%, significant Q-test, large tau2), this strategy designs the investigation protocol: subgroup analyses, meta-regression, moderator identification, and outlier diagnostics. Produces the investigation plan, not the computation.

Budget

Resource	Floor	Target
Studies identified	20	30
Effect sizes extracted	20	30
Web searches	35	50
Moderator candidates	5	10+
Quality assessments	15	30

Budget gate: cannot exit until 80% of floor met.

State Ledger

<HARD-GATE>
| Metric | Current | Floor | Target | Status |
|--------|---------|-------|--------|--------|
| Studies found | 0 | 20 | 30 | BLOCKED |
| Effect sizes planned | 0 | 20 | 30 | BLOCKED |
| Web searches done | 0 | 35 | 50 | BLOCKED |
| Moderators identified | 0 | 5 | 10+ | BLOCKED |
| Quality assessed | 0 | 15 | 30 | BLOCKED |
</HARD-GATE>

Available Tactics

Tactic	When to Use
effect-size-extraction	Extract effect sizes with full study characteristics
quality-assessment-protocol	Assess whether quality explains heterogeneity
evidence-synthesis-planning	Plan subgroup and meta-regression models

Available SOPs

SOP	When to Use
pico-formulation	Frame the heterogeneity question
inclusion-criteria-design	Broad inclusion to capture variation
effect-size-planning	Standardize for comparability
data-extraction-form	Rich moderator variable extraction
risk-of-bias-assessment	RoB as potential moderator
heterogeneity-source-analysis	Core SOP — classify heterogeneity sources
sensitivity-analysis-design	Outlier removal, influence diagnostics
publication-bias-assessment	Bias as heterogeneity source
meta-analysis-synthesis	Final investigation protocol

Execution Guidance

1. Frame — Run pico-formulation emphasizing variation in P/I/C/O
2. Scope — Run inclusion-criteria-design with broad criteria (capture variation)
3. Search — Systematic search + web research on known moderators
4. Extract — Use effect-size-extraction with rich study-level covariates
5. Hypothesize — Run heterogeneity-source-analysis to generate moderator hypotheses
6. Assess — Use quality-assessment-protocol (RoB as moderator)
7. Plan — Use evidence-synthesis-planning for subgroup + meta-regression
8. Synthesize — Run meta-analysis-synthesis for investigation protocol

Web searches focus on domain knowledge about why results might differ (methodological, clinical, statistical heterogeneity).

Output Format

protocol:
  question: [Why do studies of X reach different conclusions?]
  heterogeneity_metrics: [I2, tau2, Q-test, prediction interval]
  moderator_candidates:
    clinical: [population, intervention details, outcome timing]
    methodological: [study design, RoB, measurement tools]
    statistical: [effect size type, analysis method, sample size]
  investigation_plan:
    subgroup_analyses: [categorical moderators]
    meta_regression: [continuous moderators]
    outlier_diagnostics: [influence analysis, Baujat plot]
    sensitivity: [leave-one-out, cumulative by quality]
  a_priori_hypotheses: [pre-specified moderator hypotheses]
  multiple_testing: [correction strategy]
  reporting: PRISMA-2020 + heterogeneity reporting guidelines