How to Report Confidence Intervals in a Manuscript

A confidence interval (CI) communicates the precision of an estimate, not just whether it cleared a significance threshold. Most current reporting standards — including CONSORT 2010 and the ICMJE recommendations — now treat reporting a CI alongside every primary and secondary outcome as a requirement, not an option. This page covers exactly how to write one: the notation, the decimal precision, the differences between style guides, and the mistakes that get flagged most often in peer review.

If you need a refresher on what a confidence interval actually means or how to calculate one, see Confidence Interval Explained: How to Calculate and Interpret One first. This page assumes you already have the interval and need to know how to write it into a Results section.

Quick reference: CI notation by style guide

Style guide	Notation	Worked example	Notes
APA (7th edition)	95% CI [LL, UL]	M = 4.6, 95% CI [2.31, 6.89]	Square brackets, comma between bounds, no repeated percent sign, same decimal precision as the point estimate.
AMA / most biomedical & clinical journals	(95% CI, LL-UL) or (95% CI: LL-UL)	OR, 1.8 (95% CI, 1.1-2.9)	Parentheses, hyphen or en dash between bounds. The exact separator (comma vs. colon) varies by journal — check the target journal’s instructions for authors before submission.
CONSORT / ICMJE (style-agnostic requirement)	Point estimate with CI stated for every primary and secondary outcome	Mean difference −3.2 kg (95% CI −5.1 to −1.3)	These are reporting-completeness requirements, not notation rules — the actual formatting still follows whichever style guide (APA, AMA, Vancouver) the journal has adopted.
No house style specified	95% CI [LL, UL]	95% CI [2.3, 6.7]	The APA bracket format is the safest default when a journal gives no explicit statistics style guidance.

Why the CI has to be there, not just the p-value

Three overlapping requirements push authors toward reporting confidence intervals as standard practice rather than an optional extra:

• CONSORT 2010, the reporting guideline for randomized controlled trials, requires effect sizes and their precision (confidence intervals) to be reported for every primary and secondary outcome — not p-values reported in isolation. See the CONSORT Statement guide for the full 25-item checklist.
• ICMJE’s recommendations for manuscript preparation instruct authors, in the statistics section, to “avoid relying solely on statistical hypothesis testing, such as P values, which fail to convey important information about effect size and precision of estimates,” and to “quantify findings and present them with appropriate indicators of measurement error or uncertainty (such as confidence intervals)” whenever possible.
• APA’s Publication Manual (7th edition), in its guidance on statistical reporting, instructs authors to report an effect size and confidence interval for each primary outcome alongside significance testing — the same principle behind CASRAI’s companion guide, How to Report P Values.

The practical upshot: a Results sentence that reports only “p = .03” without an accompanying effect size and interval is incomplete by the standards most journals in the biomedical and social sciences currently enforce.

Writing the CI in text: APA style

In APA style, the confidence interval follows the point estimate, in square brackets, with the lower and upper limits separated by a comma. The percent sign and “CI” are stated once, not repeated for each bound:

Correct: “Participants in the intervention group lost significantly more weight than controls, M = 3.2 kg, 95% CI [1.1, 5.3], p = .004.”

Incorrect: “… 95% CI (1.1% – 5.3%) …” — parentheses and a percent sign on each bound are AMA/biomedical conventions, not APA’s.

Keep the decimal precision of the CI bounds consistent with the point estimate itself — if the mean is reported to one decimal place, the CI bounds should generally match rather than appearing more or less precise than the estimate they bracket.

Writing the CI in text: AMA and biomedical-journal style

AMA style and most biomedical and clinical journals place the CI in parentheses, typically after a comma or colon following “95% CI,” with the bounds separated by a hyphen or en dash rather than a comma:

Example: “Patients receiving the intervention had lower 30-day readmission rates (OR, 0.62; 95% CI, 0.41-0.94; P = .02).”

Because the exact punctuation (comma vs. colon after “CI,” hyphen vs. en dash between bounds) varies by journal even within AMA-adjacent house styles, always check the specific journal’s instructions for authors rather than assuming one biomedical journal’s convention applies to another.

Writing the CI in a table

In results tables, the CI is usually given its own column (or a bracketed sub-line under the estimate) rather than folded into a single results sentence. A typical table column header reads “95% CI” with the two bounds in one cell, separated by the same convention (comma-in-brackets for APA, hyphen-in-parentheses for AMA) used in the text. Whichever format is used, keep it identical across every row of the table — mixing “[LL, UL]” in some rows with “LL-UL” in others is one of the more common copyediting flags in review.

Reporting CIs for different types of estimates

Estimate type	What the CI describes	Example
Mean or mean difference	Plausible range for the true population mean or difference between groups	Mean difference = 3.2 kg, 95% CI [1.1, 5.3]
Proportion or percentage	Plausible range for the true population proportion	62%, 95% CI [54%, 70%]
Odds ratio (OR) / risk ratio (RR) / hazard ratio (HR)	Plausible range for the true ratio; a CI that spans 1.0 indicates the ratio is not statistically distinguishable from no effect at that confidence level	HR, 0.71 (95% CI, 0.52-0.97)
Correlation coefficient	Plausible range for the true population correlation	r = .34, 95% CI [.18, .49]

Note the ratio-specific rule: for odds ratios, risk ratios, and hazard ratios, the “no effect” value is 1.0, not 0 — a CI that includes 1.0 (e.g., 95% CI, 0.89-1.42) indicates the result is not statistically significant at that confidence level, even if the point estimate itself looks meaningfully different from 1. For mean differences and correlations, the corresponding “no effect” value is 0.

Common mistakes to check before submission

• Inconsistent notation within the same manuscript. Pick one convention (APA brackets or AMA parentheses) and use it in every table and every results sentence — don’t switch formats between the text and a table, or between sections.
• Mismatched decimal precision. A CI bound reported to more decimal places than the point estimate it belongs to reads as spurious precision.
• Contradicting the CI in the prose. Describing a result as a meaningful effect while the CI for a ratio spans 1.0 (or a CI for a difference spans 0) is an internal contradiction reviewers routinely flag.
• Omitting the confidence level. If the interval is not a 95% CI — a 90% or 99% CI, for instance — say so explicitly; “95%” is a convention, not a default that can be assumed.
• Reporting the CI for the estimate but not stating what estimate it belongs to. “95% CI [1.1, 5.3]” alone is not interpretable — it must be attached to a named point estimate (a mean difference, an odds ratio, a proportion).
• Ambiguous negative-bound formatting. A hyphen between two negative numbers (e.g., “-5.1–1.3”) is genuinely ambiguous in print. Use “to” (“−5.1 to −1.3”) or an unambiguous en dash with spacing, and check how your target journal handles this case specifically.

Frequently asked questions

What is the correct confidence interval reporting format?

There is no single universal format — it depends on the style guide the target journal follows. APA style uses square brackets with a comma (“95% CI [1.1, 5.3]”); AMA and most biomedical journals use parentheses with a hyphen (“95% CI, 1.1-5.3”). CONSORT and ICMJE require that a CI be reported for every primary and secondary outcome, but leave the exact notation to the journal’s chosen style guide.

How do I write confidence intervals in a Results section?

State the point estimate first, then the confidence interval immediately after it, in the notation your target journal’s style guide specifies, followed by the p-value if one is reported: for example, “M = 3.2 kg, 95% CI [1.1, 5.3], p = .004” in APA style, or “OR, 0.62; 95% CI, 0.41-0.94; P = .02” in AMA style. Keep the format identical across every outcome reported in the same section.

Is CI reporting in APA style different from AMA style?

Yes. APA style (7th edition) uses square brackets and a comma between the lower and upper bound, with the percent sign stated once. AMA style and most biomedical/clinical journals use parentheses, typically with a hyphen or en dash between bounds and a comma or colon after “CI.” Always confirm against the specific target journal’s instructions for authors, since biomedical journals do not apply AMA conventions with perfect uniformity.

Do I still need to report a p-value if I report a confidence interval?

Most journals and reporting guidelines expect both, not one instead of the other — the CI conveys precision and effect size, the p-value conveys the significance-test result. See How to Report P Values for the companion formatting rules.

What confidence level should I use if the journal doesn’t specify one?

95% is the near-universal default in biomedical and social-science reporting. If a different level is used (90% or 99%, for instance), state it explicitly rather than leaving the reader to assume 95%.

Last verified: 16 August 2026, against ICMJE’s recommendations for manuscript preparation and CASRAI’s own verified-facts record for the APA Publication Manual (7th edition) and CONSORT 2010 requirements. Always confirm the specific notation against your target journal’s current instructions for authors, since house style can vary even within one style-guide family.