Binary Outcome --- Class Balance Diagnostics & Association Testing

Table of Contents

• Scope Boundary
• Workflow
• Decision Tree
• Required Inputs
• Code Structure
• Reporting Standards
• Hypothesis Tests
• Example Dataset
• Method Status
• Minimal Smoke Test
• Cross-Skill Interface

Open-source skill.

Scope Boundary

Use this skill when:

• The outcome is a single binary endpoint and the first need is a defensible descriptive / inferential baseline.
• The main question is a cross-sectional association or simple group comparison, not a full prediction workflow.

Do not use this skill when:

• The design is paired, matched, or otherwise within-subject; use vera-data-repeated-reviewing.
• The target is ordinal, nominal, count, survival, or time-to-event rather than binary.

Workflow

Read each step file in workflow/ before executing that step.

Step	Responsibility	Executor	Document	Input	Output
Collect	Collect Inputs	Main Agent	workflow/step01-collect-inputs.md	User input	Structured input summary
Diagnose	Check Distribution	Main Agent	workflow/step02-check-distribution.md	Prior step output	PART 1 code block
Test	Run Primary Test	Main Agent	workflow/step03-run-primary-test.md	Prior step output	PART 2-3 code blocks

Decision Tree

1. CHECK CLASS BALANCE
   ├── Balanced (minority ≥ 10%) → standard tests
   └── Imbalanced (minority < 10%) → rare event warning, note power limits

2. PRIMARY ASSOCIATION TEST
   ├── All cells ≥ 5 → Chi-square + Cramer's V + OR
   └── Any cell < 5 → Fisher's exact + OR

Required Inputs

Role	What to collect
Outcome (Y)	Variable name, what 0/1 represents
Primary group variable	What defines groups, how many levels
Predictors	For recommendation block (not executed)
Covariates	For recommendation block (not executed)

Code Structure

PART 0: Setup & Data Loading
PART 1: Class Balance Diagnostics  → plot_01_class_balance.png
PART 2: Primary Association Test   → plot_02_mosaic_[var].png
PART 3: Recommendation Block       → text listing additional analyses available

Reporting Standards

1. p-values: "< .001" not "0.000"; exact to 3 decimals otherwise
2. Effect sizes: Cramer's V (chi-square), odds ratio with 95% CI
3. Odds ratios: always as "OR = X.XX, 95% CI [X.XX, X.XX]"
4. Proportions: report as percentages with 1 decimal
5. Chi-square: chi-sq(df) = X.XX, p = .XXX, Cramer's V = .XXX
6. Degrees of freedom: always with chi-square statistic
7. Sample size: final analytic N
8. Decimal places: 1 for proportions, 2 for OR, 3 for p and effect sizes
9. Non-significance: "not statistically significant at alpha = .05" --- never "no association"

Hypothesis Tests

Scenario	Expected cells all >= 5	Any expected cell < 5
2x2 or 2xK	Chi-square + Cramer's V	Fisher's exact test

Paired/matched binary designs -> vera-data-repeated-reviewing (handles within-subject comparisons including paired binary data via McNemar's test).

Example Dataset

R built-in Titanic (convert to data frame): outcome = Survived (0/1), predictors = Class, Sex, Age. Python: sm.datasets.get_rdataset("Titanic").data or reconstruct from counts (offline fallback uses base R Titanic dataset).

Method Status

Status	Methods
Implemented in this skill	Class-balance diagnostics, chi-square / Fisher's exact testing, Cramer's V, odds ratio with 95% CI
Implemented downstream in vera-data-binary-generating	Additional association tests, stratified odds ratios, logistic regression, ROC/AUC summaries, exploratory tree-based models
Out of scope in this open-source baseline	Matched binary workflows, causal estimands, and any binary method not named above

Minimal Smoke Test

• Smoke-test prompt: "Run vera-data-binary-reviewing on Titanic, treating Survived as the outcome and Sex as the primary grouping variable. Produce the standard baseline artifacts."

Cross-Skill Interface

Output:
├── code_r      → .R script
├── code_python → .py script
├── figures/    → 2 PNGs (class balance + mosaic/grouped bar)
└── recommendations → text block (additional analyses available)

Next step: Invoke vera-data-binary-generating from this skillset to run the full pipeline (additional tests, subgroup analysis, modeling, manuscript generation). See ../../CROSS-SKILL-INTERFACE.md for the shared handoff contract.