spec: add funnel-meta-analysis specification (#4609)

## New Specification: `funnel-meta-analysis`

Related to #4590

---

### specification.md

# funnel-meta-analysis: Meta-Analysis Funnel Plot for Publication Bias

## Description

A funnel plot used in meta-analysis to assess publication bias by
plotting individual study effect sizes against their precision
(typically standard error). Studies scatter around a summary effect
line, with pseudo 95% confidence limits forming an inverted funnel
shape. In the absence of bias, studies distribute symmetrically around
the summary effect; asymmetry suggests publication bias or systematic
heterogeneity. This is a standard tool in systematic reviews and
Cochrane-style meta-analyses.

## Applications

- Systematic review authors assessing whether small-study effects
indicate publication bias across included trials
- Cochrane reviewers generating standard funnel plots as part of
required reporting for intervention reviews
- Research methodologists evaluating selective reporting by visually
inspecting funnel asymmetry
- Epidemiologists checking meta-analytic robustness before drawing
pooled conclusions

## Data

- `effect_size` (float) - Point estimate from each study (e.g., odds
ratio, mean difference, risk ratio)
- `std_error` (float) - Standard error of each study's effect estimate
- `study` (str, optional) - Study label or identifier for annotation
- Size: 8-30 studies
- Example: Meta-analysis of 15 randomized controlled trials comparing
drug vs placebo, with log odds ratios and standard errors

## Notes

- Y-axis shows standard error (inverted so that larger/more precise
studies appear at the top)
- X-axis shows the effect size measure
- Draw a vertical line at the summary/pooled effect size
- Draw pseudo 95% confidence limits as diagonal lines forming the funnel
shape (summary effect +/- 1.96 * SE)
- Plot individual studies as points (optionally sized by weight or
sample size)
- Include a vertical dashed reference line at the null effect (0 for
differences, 1 for ratios) if different from summary effect
- Asymmetry in the scatter pattern suggests publication bias

---

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plots/funnel-meta-analysis/specification.md

@@ -0,0 +1,30 @@
+# funnel-meta-analysis: Meta-Analysis Funnel Plot for Publication Bias
+
+## Description
+
+A funnel plot used in meta-analysis to assess publication bias by plotting individual study effect sizes against their precision (typically standard error). Studies scatter around a summary effect line, with pseudo 95% confidence limits forming an inverted funnel shape. In the absence of bias, studies distribute symmetrically around the summary effect; asymmetry suggests publication bias or systematic heterogeneity. This is a standard tool in systematic reviews and Cochrane-style meta-analyses.
+
+## Applications
+
+- Systematic review authors assessing whether small-study effects indicate publication bias across included trials
+- Cochrane reviewers generating standard funnel plots as part of required reporting for intervention reviews
+- Research methodologists evaluating selective reporting by visually inspecting funnel asymmetry
+- Epidemiologists checking meta-analytic robustness before drawing pooled conclusions
+
+## Data
+
+- `effect_size` (float) - Point estimate from each study (e.g., odds ratio, mean difference, risk ratio)
+- `std_error` (float) - Standard error of each study's effect estimate
+- `study` (str, optional) - Study label or identifier for annotation
+- Size: 8-30 studies
+- Example: Meta-analysis of 15 randomized controlled trials comparing drug vs placebo, with log odds ratios and standard errors
+
+## Notes
+
+- Y-axis shows standard error (inverted so that larger/more precise studies appear at the top)
+- X-axis shows the effect size measure
+- Draw a vertical line at the summary/pooled effect size
+- Draw pseudo 95% confidence limits as diagonal lines forming the funnel shape (summary effect +/- 1.96 * SE)
+- Plot individual studies as points (optionally sized by weight or sample size)
+- Include a vertical dashed reference line at the null effect (0 for differences, 1 for ratios) if different from summary effect
+- Asymmetry in the scatter pattern suggests publication bias

plots/funnel-meta-analysis/specification.yaml

@@ -0,0 +1,29 @@
+# Specification-level metadata for funnel-meta-analysis
+# Auto-synced to PostgreSQL on push to main
+
+spec_id: funnel-meta-analysis
+title: Meta-Analysis Funnel Plot for Publication Bias
+
+# Specification tracking
+created: "2026-03-06T19:55:04Z"
+updated: null
+issue: 4590
+suggested: MarkusNeusinger
+
+# Classification tags (applies to all library implementations)
+# See docs/reference/tagging-system.md for detailed guidelines
+tags:
+  plot_type:
+    - scatter
+    - funnel
+  data_type:
+    - numeric
+    - continuous
+  domain:
+    - statistics
+    - healthcare
+    - research
+  features:
+    - annotated
+    - comparison
+    - confidence-interval