# Nejm Statistics

> Use to enforce NEJM's clinical statistical reporting — confidence intervals over bare P values, the pre-specified intention-to-treat primary analysis, multiplicity control for secondary endpoints, pre-specified subgroups with interaction tests, missing-data handling, and absolute risk with NNT alongside relative measures.

- Skill: `thedixitjain/nejm-statistics` (Agent Skill)
- Install (CLI): `npx skillmds add thedixitjain/nejm-statistics`
- Raw SKILL.md: https://api.skillmd.com/api/skills/thedixitjain/nejm-statistics/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: thedixitjain (https://skillmd.com/u/thedixitjain)
- Updated: 2026-09-08
- Page: https://skillmd.com/skills/thedixitjain/nejm-statistics

---



# Clinical Statistics & Reporting (nejm-statistics)

## When to trigger

- Results report P values without confidence intervals.
- The primary analysis population (ITT vs per-protocol) is unclear.
- Many secondary endpoints are tested with no multiplicity plan.
- Subgroup findings are highlighted without pre-specification or interaction tests.
- Only relative risk is reported, with no absolute risk or NNT.

## Confidence intervals over bare P values

NEJM's statistical reporting guidance favors **effect estimates with 95% confidence intervals** over bare significance tests.

- [ ] Every primary and key secondary outcome: **effect estimate + 95% CI** (HR/RR/OR or mean difference).
- [ ] Report **exact P values** (e.g., P=0.03), not "P<0.05", except for very small values.
- [ ] A CI that includes the null is not "no difference" — report the estimate and its width; interpret precision.
- [ ] For observational data, use **cautious, non-causal language** (associated with, not causes).

## The pre-specified primary analysis

- The **primary outcome** is single and pre-specified; its analysis follows the SAP.
- **Intention-to-treat** is the primary analysis population for superiority trials; **per-protocol** is a sensitivity analysis. (For non-inferiority, both ITT and per-protocol matter — report both.)
- State the analysis model (e.g., Cox, logistic, mixed model) and pre-specified covariates/stratification.

## Multiplicity (the secondary-endpoint trap)

- Pre-specify a **testing hierarchy** or a multiplicity adjustment (e.g., gatekeeping, Hochberg, Bonferroni) for multiple primary/secondary endpoints.
- Endpoints **not** in the controlled testing scheme are **exploratory** — say so, and report estimates with CIs but no inferential P claims.
- Do not declare a secondary endpoint "significant" if it sits outside the multiplicity plan.

## Subgroups (warn against over-interpretation)

- Subgroup analyses must be **pre-specified**; label post-hoc subgroups as exploratory.
- Test the **interaction** (treatment × subgroup), not just within-subgroup P values — a within-subgroup "significant" effect without a significant interaction is weak evidence.
- Present subgroups in a **forest plot** with interaction P values (see `nejm-figures-tables`).
- Do not let a subgroup result become the headline of an otherwise null trial.

## Absolute risk and NNT

- Report **absolute risk difference** alongside relative measures — a large relative reduction on a rare outcome can be a tiny absolute one.
- Where clinically meaningful, give the **number needed to treat (NNT)** (or number needed to harm).
- For safety, report **absolute event rates** by arm, not relative comparisons alone.

## Missing data, survival, and other essentials

- State the **amount and pattern of missing data** and the handling (e.g., multiple imputation); avoid naive last-observation-carried-forward as the primary approach.
- **Time-to-event**: Kaplan–Meier with numbers-at-risk; Cox model with the proportional-hazards assumption checked; report median follow-up.
- Pre-specify **interim analyses / stopping boundaries**; report them if a DSMB acted.
- For non-inferiority: state the pre-specified **margin** and its justification.

## What the statistical reviewer probes

NEJM routinely assigns trials a dedicated statistical reviewer (see `nejm-rebuttal`). Pre-empt the line items:

- [ ] **SAP concordance** — every analysis traces to the pre-specified SAP; deviations listed and dated.
- [ ] **Event counts behind every ratio** — per-arm numerators and denominators for every reported estimate.
- [ ] **CI width, not just position** — an interval spanning trivial and decisive effects is inconclusive.
- [ ] **Assumptions checked** — proportional hazards verified; how stratification variables entered the model.
- [ ] **Cross-location consistency** — the same estimate, to the same decimal, in abstract, text, tables, and figures.

## Worked micro-example — a subgroup claim (before → after)

- Before: "The benefit was significant in patients older than 65 years (P=0.04) but not younger (P=0.31), so older patients should receive the drug."
- After: "The hazard ratio was 0.68 (95% CI, 0.47 to 0.98) among patients older than 65 years and 0.89 (95% CI, 0.64 to 1.24) among younger patients (P=0.29 for interaction)."

The estimates, CIs, and interaction test replace significance chatter; the nonsignificant interaction disciplines the conclusion. (Numbers invented.)

## Output format

```
【Per-outcome reporting】 effect + 95% CI present for primary + key secondary? gaps: [...]
【Statistical-reviewer preflight】 SAP concordance / event counts / assumptions / cross-location consistency? yes/no
【Primary analysis population】 ITT primary? per-protocol as sensitivity? yes/no
【Multiplicity】 hierarchy/adjustment pre-specified? exploratory endpoints labeled? yes/no
【Subgroups】 pre-specified? interaction tests reported? over-interpretation flags: [...]
【Absolute risk + NNT】 reported alongside relative measures? yes/no
【Missing data / survival / non-inferiority margin】 handled & stated? yes/no
【Causal language (observational)】 appropriately cautious? yes/no
【Next】 nejm-figures-tables
```

## Anti-patterns

- **Do not** report relative risk without absolute risk for clinical outcomes.
- **Do not** declare secondary or subgroup endpoints significant outside the multiplicity plan.
- **Do not** infer "no effect" from a wide CI crossing the null on an underpowered comparison.
- **Do not** use causal verbs ("reduced", "caused") for observational associations.
- **Do not** make per-protocol the primary analysis in a superiority trial.

---

**Source:** [`brycewang-stanford/Awesome-Journal-Skills`](https://github.com/brycewang-stanford/Awesome-Journal-Skills) → `NEJM-Skills/skills/nejm-statistics/SKILL.md`